diff --git a/src/js/background.js b/src/js/background.js
index 2e07228f..7ca05f30 100644
--- a/src/js/background.js
+++ b/src/js/background.js
@@ -116,7 +116,28 @@ brws.runtime.onStartup.addListener(() => {
   brws.storage.local.set({ version: brws.runtime.getManifest().version });
 });
 
-brws.runtime.onMessage.addListener((request, _, sendResponse) => {
+// Fields the crowd-contribute/query bridge accepts, matching the documented
+// signature of crowdQuery/crowdContribute in helpers/dom.js. Anything else in
+// request.detail is dropped rather than forwarded -- the content-script bridge
+// has no way to verify the message actually came from the extension's own
+// injected script rather than the hosting page itself (see security advisory
+// GHSA-vw3r-qv4c-vw79 / GHSA-5vfw-qqg5-35wj-style report), so background.js is
+// the last point that can still enforce a shape on what gets sent out.
+const CROWD_FIELDS = {
+  crowdQuery: ['domain', 'path'],
+  crowdContribute: ['domain', 'path', 'target'],
+  followAndContribute: ['domain', 'path', 'target'],
+};
+
+brws.runtime.onMessage.addListener((request, sender, sendResponse) => {
+  if (request.type === 'getTabId') {
+    // sender.tab.id is populated by the browser itself from the real
+    // connection the message arrived on -- a page script cannot forge it,
+    // unlike anything carried in a CustomEvent's `detail`.
+    sendResponse(sender.tab ? sender.tab.id : null);
+    return false;
+  }
+
   (async () => {
     let options = await getOptions();
     if (options.optionCrowdBypass === false) {
@@ -127,14 +148,24 @@ brws.runtime.onMessage.addListener((request, _, sendResponse) => {
       ? (url = 'https://crowd.fastforward.team/crowd/query_v1')
       : (url = 'https://crowd.fastforward.team/crowd/contribute_v1');
 
+    const allowedFields = CROWD_FIELDS[request.type];
+    if (!allowedFields) {
+      return;
+    }
+
     let params = new URLSearchParams();
 
     if (request.type !== 'followAndContribute') {
-      for (let key in request.detail) {
-        params.append(key, request.detail[key]);
+      for (let key of allowedFields) {
+        if (Object.prototype.hasOwnProperty.call(request.detail, key)) {
+          params.append(key, request.detail[key]);
+        }
       }
     } else {
-      for (let key in request.detail) {
+      for (let key of allowedFields) {
+        if (!Object.prototype.hasOwnProperty.call(request.detail, key)) {
+          continue;
+        }
         if (key === 'target') {
           let dest = new URL(request.detail[key]);
           if (!fetchDomains.includes(dest.hostname)) {
diff --git a/src/js/content_script.js b/src/js/content_script.js
index f42b49a0..6968f307 100644
--- a/src/js/content_script.js
+++ b/src/js/content_script.js
@@ -1,4 +1,16 @@
 const brws = typeof browser !== 'undefined' ? browser : chrome;
+
+// ffclipboard keys are namespaced by the real tab id, as reported by the
+// browser itself via background.js's sender.tab.id -- a page script cannot
+// forge this the way it can forge a CustomEvent's `detail`. This stops an
+// unrelated tab/page from reading or poisoning another tab's in-flight
+// ffclipboard state.
+const ffClipboardTabId = brws.runtime.sendMessage({ type: 'getTabId' });
+async function ffClipboardKey(key) {
+  const tabId = await ffClipboardTabId;
+  return `${tabId}:${key}`;
+}
+
 async function getOptions() {
   return new Promise((resolve) => {
     brws.storage.local.get('options').then((result) => {
@@ -71,19 +83,21 @@ document.addEventListener('ff53054c0e13_followAndContribute', (event) => {
   });
 });
 
-function onFFClipboardSet(event) {
+async function onFFClipboardSet(event) {
   const { key, value } = event.detail;
+  const scopedKey = await ffClipboardKey(key);
   chrome.storage.local.get('ffclipboard', (result) => {
     const ffclipboard = result.ffclipboard || {};
-    ffclipboard[key] = value;
+    ffclipboard[scopedKey] = value;
     chrome.storage.local.set({ ffclipboard });
   });
 }
 
-function onFFClipboardGet(event) {
+async function onFFClipboardGet(event) {
   const { key } = event.detail;
+  const scopedKey = await ffClipboardKey(key);
   chrome.storage.local.get('ffclipboard', (result) => {
-    const value = result.ffclipboard ? result.ffclipboard[key] : undefined;
+    const value = result.ffclipboard ? result.ffclipboard[scopedKey] : undefined;
     const responseEvent = new CustomEvent('ff53054c0e13_ffclipboardResponse', {
       detail: { key, value },
     });
@@ -91,11 +105,12 @@ function onFFClipboardGet(event) {
   });
 }
 
-function onFFClipboardClear(event) {
+async function onFFClipboardClear(event) {
   const { key } = event.detail;
+  const scopedKey = await ffClipboardKey(key);
   chrome.storage.local.get('ffclipboard', (result) => {
     if (result.ffclipboard) {
-      delete result.ffclipboard[key];
+      delete result.ffclipboard[scopedKey];
       chrome.storage.local.set({ ffclipboard: result.ffclipboard });
     }
   });