diff --git a/ext/src/_locales/en/messages.json b/ext/src/_locales/en/messages.json
index d3d9dec..ae885cf 100755
--- a/ext/src/_locales/en/messages.json
+++ b/ext/src/_locales/en/messages.json
@@ -329,10 +329,6 @@
         "message": "Add Item",
         "description": "Add new whitelist item button title."
     },
-    "optionsSiteWhitelistUserAgent": {
-        "message": "Disable UA",
-        "description": "Whitelist item user agent checkbox title."
-    },
     "optionsSiteWhitelistEditItem": {
         "message": "Edit",
         "description": "Edit whitelist item button title. Displayed on each item."
@@ -350,13 +346,29 @@
         "description": "Default <option> for knownApps <select>."
     },
     "optionsSiteWhitelistCustomUserAgent": {
-        "message": "Custom user agent:",
+        "message": "User agent:",
         "description": "Custom user agent option label."
     },
     "optionsSiteWhitelistCustomUserAgentDescription": {
         "message": "If specified, a custom user agent string to use for whitelisted sites.",
         "description": "Custom user agent option description."
     },
+    "optionsSiteWhitelistUserAgentDisabled": {
+        "message": "Disable user agent",
+        "description": "Whitelist item user agent disabled checkbox label."
+    },
+    "optionsSiteWhitelistUserAgentDisabledDescription": {
+        "message": "Entirely disable user agent replacement for sites matching this pattern.",
+        "description": "Whitelist item user agent disabled checkbox description."
+    },
+    "optionsSiteWhitelistSiteSpecificUserAgent": {
+        "message": "User agent:",
+        "description": "Whitelist item user agent option label."
+    },
+    "optionsSiteWhitelistSiteSpecificUserAgentDescription": {
+        "message": "If specified, a custom user agent string to use specifically for this sites matching this pattern.",
+        "description": "Whitelist item user agent option label."
+    },
 
     "optionsMirroringCategoryName": {
         "message": "Screen/tab casting",
diff --git a/ext/src/background/whitelist.ts b/ext/src/background/whitelist.ts
index 9dc3cf6..18cd009 100644
--- a/ext/src/background/whitelist.ts
+++ b/ext/src/background/whitelist.ts
@@ -4,6 +4,7 @@ import logger from "../lib/logger";
 import options from "../lib/options";
 
 import { getChromeUserAgent } from "../lib/userAgents";
+import { RemoteMatchPattern } from "../lib/matchPattern";
 
 import {
     CAST_FRAMEWORK_LOADER_SCRIPT_URL,
@@ -25,6 +26,7 @@ type OnBeforeRequestDetails = Parameters<
 export interface WhitelistItemData {
     pattern: string;
     isUserAgentDisabled?: boolean;
+    customUserAgent?: string;
 }
 
 const originUrlCache: string[] = [];
@@ -33,6 +35,8 @@ let platform: string;
 let chromeUserAgent: string | undefined;
 let chromeUserAgentHybrid: string | undefined;
 
+let siteWhitelistEnabled = false;
+let siteWhitelist: Nullable<WhitelistItemData[]> = null;
 let customUserAgent: string | undefined;
 
 export async function initWhitelist() {
@@ -65,7 +69,6 @@ export async function initWhitelist() {
         if (alteredOpts.includes("siteWhitelistCustomUserAgent")) {
             customUserAgent = await options.get("siteWhitelistCustomUserAgent");
         }
-
         if (
             alteredOpts.includes("siteWhitelist") ||
             alteredOpts.includes("siteWhitelistEnabled")
@@ -76,6 +79,30 @@ export async function initWhitelist() {
     });
 }
 
+/**
+ * Returns the configured user agent matching the specified URL or
+ * undefined if the user agent is disabled.
+ */
+function getUserAgent(url: string, host?: string): Optional<string> {
+    if (!siteWhitelistEnabled || !siteWhitelist) return;
+
+    // Search site-specific user agents
+    const matchingItem = siteWhitelist.find(
+        item =>
+            item.customUserAgent &&
+            new RemoteMatchPattern(item.pattern).matches(url)
+    );
+    if (matchingItem) {
+        if (matchingItem.isUserAgentDisabled) return;
+        return matchingItem.customUserAgent;
+    }
+
+    return (
+        customUserAgent ||
+        (host === "www.youtube.com" ? chromeUserAgentHybrid : chromeUserAgent)
+    );
+}
+
 /**
  * Web apps usually only load the sender library and
  * provide cast functionality if the browser is detected
@@ -99,11 +126,7 @@ async function onWhitelistedBeforeSendHeaders(
 
     for (const header of details.requestHeaders) {
         if (header.name === "User-Agent") {
-            header.value =
-                customUserAgent ||
-                (host?.value === "www.youtube.com"
-                    ? chromeUserAgentHybrid
-                    : chromeUserAgent);
+            header.value = getUserAgent(details.url, host?.value);
             break;
         }
     }
@@ -134,11 +157,7 @@ function onWhitelistedChildBeforeSendHeaders(
 
             for (const header of details.requestHeaders) {
                 if (header.name === "User-Agent") {
-                    header.value =
-                        customUserAgent ||
-                        (host?.value === "www.youtube.com"
-                            ? chromeUserAgentHybrid
-                            : chromeUserAgent);
+                    header.value = getUserAgent(details.url, host?.value);
                     break;
                 }
             }
@@ -205,7 +224,9 @@ async function onBeforeCastSDKRequest(details: OnBeforeRequestDetails) {
 }
 
 async function registerSiteWhitelist() {
-    const { siteWhitelist, siteWhitelistEnabled } = await options.getAll();
+    const opts = await options.getAll();
+    siteWhitelist = opts.siteWhitelist;
+    siteWhitelistEnabled = opts.siteWhitelistEnabled;
 
     browser.webRequest.onBeforeRequest.addListener(
         onBeforeCastSDKRequest,
diff --git a/ext/src/ui/options/Options.svelte b/ext/src/ui/options/Options.svelte
index 5bda111..4ece5f4 100644
--- a/ext/src/ui/options/Options.svelte
+++ b/ext/src/ui/options/Options.svelte
@@ -18,11 +18,12 @@
     let isFormValid = true;
     let isSavedIndicatorVisible = false;
 
-    let platform: string;
+    let defaultUserAgent: Optional<string>;
 
     let opts: Options | undefined;
     onMount(async () => {
-        platform = (await browser.runtime.getPlatformInfo()).os;
+        const platform = (await browser.runtime.getPlatformInfo()).os;
+        defaultUserAgent = getChromeUserAgent(platform);
 
         opts = await options.getAll();
         options.addEventListener("changed", async () => {
@@ -45,6 +46,9 @@
                 if (item.isUserAgentDisabled === false) {
                     delete item.isUserAgentDisabled;
                 }
+                if (item.customUserAgent === "") {
+                    delete item.customUserAgent;
+                }
             }
 
             await options.setAll(opts);
@@ -68,7 +72,7 @@
     }
 </script>
 
-{#if opts && platform}
+{#if opts}
     <form
         id="form"
         bind:this={formElement}
@@ -281,7 +285,7 @@
                         id="siteWhitelistCustomUserAgent"
                         type="text"
                         bind:value={opts.siteWhitelistCustomUserAgent}
-                        placeholder={getChromeUserAgent(platform)}
+                        placeholder={defaultUserAgent}
                     />
                     <div class="option__description">
                         {_("optionsSiteWhitelistCustomUserAgentDescription")}
@@ -294,7 +298,11 @@
                     {_("optionsSiteWhitelistContent")}
                 </div>
                 <div class="option__control">
-                    <Whitelist bind:items={opts.siteWhitelist} />
+                    <Whitelist
+                        bind:items={opts.siteWhitelist}
+                        {opts}
+                        {defaultUserAgent}
+                    />
                 </div>
             </div>
         </fieldset>
diff --git a/ext/src/ui/options/Whitelist.svelte b/ext/src/ui/options/Whitelist.svelte
index 7ce9468..9fa178a 100644
--- a/ext/src/ui/options/Whitelist.svelte
+++ b/ext/src/ui/options/Whitelist.svelte
@@ -4,11 +4,14 @@
     import knownApps, { KnownApp } from "../../cast/knownApps";
     import { WhitelistItemData } from "../../background/whitelist";
     import { REMOTE_MATCH_PATTERN_REGEX } from "../../lib/matchPattern";
+    import { Options } from "../../lib/options";
 
     const _ = browser.i18n.getMessage;
 
     /** Whitelist items to display. */
     export let items: WhitelistItemData[];
+    export let opts: Options;
+    export let defaultUserAgent: Optional<string>;
 
     let isEditing = false;
     let isEditingValid = false;
@@ -16,6 +19,8 @@
     let editingInput: HTMLInputElement;
     let editingValue: string;
 
+    let expandedItemIndices = new Set();
+
     let knownAppToAdd: Nullable<KnownApp> = null;
     $: filteredKnownApps = Object.values(knownApps).filter(app => {
         // If no pattern or name matches default media sender
@@ -115,13 +120,17 @@
     <ul class="whitelist__items">
         {#each items as item, i}
             {@const isEditingItem = isEditing && editingIndex === i}
+            {@const isItemExpanded = expandedItemIndices.has(i)}
 
             <li
                 class="whitelist__item"
                 class:whitelist__item--selected={isEditingItem}
-                on:dblclick={() => beginEditing(i)}
+                class:whitelist__item--expanded={isItemExpanded}
             >
-                <div class="whitelist__title">
+                <div
+                    class="whitelist__title"
+                    on:dblclick={() => beginEditing(i)}
+                >
                     {#if isEditingItem}
                         <input
                             type="text"
@@ -150,13 +159,6 @@
                 </div>
 
                 {#if !isEditingItem}
-                    <label class="whitelist__user-agent">
-                        <input
-                            type="checkbox"
-                            bind:checked={item.isUserAgentDisabled}
-                        />
-                        {_("optionsSiteWhitelistUserAgent")}
-                    </label>
                     <button
                         type="button"
                         class="whitelist__edit-button ghost"
@@ -177,6 +179,80 @@
                 >
                     <img src="assets/photon_delete.svg" alt="icon, remove" />
                 </button>
+
+                {#if !isEditingItem}
+                    <button
+                        type="button"
+                        class="whitelist__expand-button ghost"
+                        title={_("optionsSiteWhitelistRemoveItem")}
+                        on:click={() => {
+                            // Toggle expanded state
+                            if (isItemExpanded) {
+                                expandedItemIndices.delete(i);
+                            } else {
+                                expandedItemIndices.add(i);
+                            }
+                            expandedItemIndices = expandedItemIndices;
+                        }}
+                    >
+                        <img
+                            src="assets/{isItemExpanded
+                                ? 'photon_arrowhead_up.svg'
+                                : 'photon_arrowhead_down.svg'}"
+                            alt="icon, arrow down"
+                        />
+                    </button>
+
+                    {#if isItemExpanded}
+                        <div class="whitelist__expanded">
+                            <div class="option option--inline">
+                                <div class="option__control">
+                                    <input
+                                        id="isUserAgentDisabled-{i}"
+                                        type="checkbox"
+                                        bind:checked={item.isUserAgentDisabled}
+                                    />
+                                </div>
+                                <label
+                                    class="option__label"
+                                    for="isUserAgentDisabled-{i}"
+                                >
+                                    {_("optionsSiteWhitelistUserAgentDisabled")}
+                                </label>
+                                <div class="option__description">
+                                    {_(
+                                        "optionsSiteWhitelistUserAgentDisabledDescription"
+                                    )}
+                                </div>
+                            </div>
+
+                            <div class="option">
+                                <label
+                                    class="option__label"
+                                    for="customUserAgentString-{i}"
+                                >
+                                    {_(
+                                        "optionsSiteWhitelistSiteSpecificUserAgent"
+                                    )}
+                                </label>
+                                <div class="option__control">
+                                    <input
+                                        id="customUserAgentString-{i}"
+                                        type="text"
+                                        bind:value={item.customUserAgent}
+                                        placeholder={opts.siteWhitelistCustomUserAgent ||
+                                            defaultUserAgent}
+                                    />
+                                    <div class="option__description">
+                                        {_(
+                                            "optionsSiteWhitelistSiteSpecificUserAgentDescription"
+                                        )}
+                                    </div>
+                                </div>
+                            </div>
+                        </div>
+                    {/if}
+                {/if}
             </li>
         {/each}
     </ul>
diff --git a/ext/src/ui/options/assets/photon_arrowhead_down.svg b/ext/src/ui/options/assets/photon_arrowhead_down.svg
new file mode 100644
index 0000000..6df37f8
--- /dev/null
+++ b/ext/src/ui/options/assets/photon_arrowhead_down.svg
@@ -0,0 +1,13 @@
+<!-- This Source Code Form is subject to the terms of the Mozilla Public
+   - License, v. 2.0. If a copy of the MPL was not distributed with this
+   - file, You can obtain one at http://mozilla.org/MPL/2.0/. -->
+<svg xmlns="http://www.w3.org/2000/svg" width="16" height="16" viewBox="0 0 16 16">
+    <style>
+        @media (prefers-color-scheme: dark) {
+            path {
+                fill: rgba(249, 249, 250, .8);
+            }
+        }
+    </style>
+   <path fill="rgba(12, 12, 13, .8)" d="M8 12a1 1 0 0 1-.707-.293l-5-5a1 1 0 0 1 1.414-1.414L8 9.586l4.293-4.293a1 1 0 0 1 1.414 1.414l-5 5A1 1 0 0 1 8 12z"></path>
+</svg>
diff --git a/ext/src/ui/options/assets/photon_arrowhead_up.svg b/ext/src/ui/options/assets/photon_arrowhead_up.svg
new file mode 100644
index 0000000..ad272f6
--- /dev/null
+++ b/ext/src/ui/options/assets/photon_arrowhead_up.svg
@@ -0,0 +1,13 @@
+<!-- This Source Code Form is subject to the terms of the Mozilla Public
+   - License, v. 2.0. If a copy of the MPL was not distributed with this
+   - file, You can obtain one at http://mozilla.org/MPL/2.0/. -->
+<svg xmlns="http://www.w3.org/2000/svg" width="16" height="16" viewBox="0 0 16 16">
+    <style>
+        @media (prefers-color-scheme: dark) {
+            path {
+                fill: rgba(249, 249, 250, .8);
+            }
+        }
+    </style>
+   <path fill="rgba(12, 12, 13, .8)" d="M13 11a1 1 0 0 1-.707-.293L8 6.414l-4.293 4.293a1 1 0 0 1-1.414-1.414l5-5a1 1 0 0 1 1.414 0l5 5A1 1 0 0 1 13 11z"></path>
+</svg>
\ No newline at end of file
diff --git a/ext/src/ui/options/styles/index.css b/ext/src/ui/options/styles/index.css
index d94c5c7..230ec1a 100644
--- a/ext/src/ui/options/styles/index.css
+++ b/ext/src/ui/options/styles/index.css
@@ -1,11 +1,11 @@
 :root {
-    --border-color: rgb(225, 225, 225);
+    --border-color: var(--grey-90-a20);
     --secondary-color: rgb(125, 125, 125);
 }
 
 @media (prefers-color-scheme: dark) {
     :root {
-        --border-color: var(--grey-50);
+        --border-color: var(--grey-10-a20);
         --secondary-color: var(--grey-10-a60);
     }
 }
@@ -223,10 +223,6 @@ button.ghost:not(:hover) {
     padding: 10px 0;
 }
 
-.category:disabled {
-    color: var(--secondary-color);
-}
-
 #form > .category {
     border-bottom: 1px solid var(--border-color);
 }
@@ -350,13 +346,13 @@ button.ghost:not(:hover) {
 .whitelist__item {
     align-items: center;
     display: flex;
-    gap: 5px;
-    height: 34px;
+    flex-wrap: wrap;
+    column-gap: 5px;
     padding: 0 10px;
 }
 
 .whitelist__item:nth-child(even) {
-    background-color: rgba(0, 0, 0, 0.05);
+    background-color: rgba(0, 0, 0, 0.1);
 }
 
 .whitelist__item--selected {
@@ -365,7 +361,9 @@ button.ghost:not(:hover) {
 
 .whitelist__title {
     display: flex;
+    align-items: center;
     flex: 1;
+    min-height: 34px;
     min-width: 0;
     padding: 4px;
     white-space: nowrap;
@@ -389,6 +387,16 @@ button.ghost:not(:hover) {
     margin-inline-end: auto;
 }
 
+.whitelist__expanded {
+    border-top: 1px solid var(--border-color);
+    display: grid;
+    grid-template-columns: 80px minmax(0, 1fr);
+    grid-column-gap: 10px;
+    grid-row-gap: 5px;
+    padding: 10px;
+    width: 100%;
+}
+
 .translator__tag {
     color: #0a84ff;
     display: inline-block;
@@ -399,7 +407,9 @@ button.ghost:not(:hover) {
     vertical-align: text-top;
 }
 
-#siteWhitelistCustomUserAgent {
+/* Option specific styles */
+#siteWhitelistCustomUserAgent,
+input[id^="customUserAgentString-"] {
     width: -moz-available;
 }