Prevent stale Add-ons removal from deleting replacement

app/scripts/fetch_xulrunner

@@ -460,6 +460,31 @@ function modify_omni {
 	replace_line 'let \{ BrowserAddonUI \} = windowRoot.window;' '' $file
 	replace_line 'await BrowserAddonUI.promptRemoveExtension' 'promptRemoveExtension' $file
 
+	file="chrome/toolkit/content/mozapps/extensions/components/addon-list.mjs"
+	# The Add-ons window can retain the old add-on wrapper after a replacement.
+	# Finalizing that wrapper's pending uninstall would remove the new copy by ID.
+	replace_line '  disconnectedCallback\(\) \{' '  async disconnectedCallback() {' $file
+	remove_line '    this.pendingUninstallAddons.clear\(\);' $file
+	replace_line '    for \(const addon of this.pendingUninstallAddons\) \{' \
+		'    const pendingUninstalls = [...this.pendingUninstallAddons];
+    this.pendingUninstallAddons.clear();
+    for (const addon of pendingUninstalls) {' $file
+	replace_line '      if \(isPending\(addon, "uninstall"\)\) \{' \
+		'      const current = await AddonManager.getAddonByID(addon.id);
+      if (this.isConnected) {
+        return;
+      }
+      if (current === addon && isPending(current, "uninstall")) {' $file
+	replace_line '  onInstalled\(addon\) \{' '  onInstalled(addon) {
+    if (!isPending(addon, "uninstall")) {
+      for (const pending of this.pendingUninstallAddons) {
+        if (pending.id === addon.id) {
+          this.pendingUninstallAddons.delete(pending);
+          this.removePendingUninstallBar(pending);
+        }
+      }
+    }' $file
+
 	# Customize empty-list message
 	replace_line 'createEmptyListMessage\(\) {' 'createEmptyListMessage() {
         var p = document.createElement("p");

app/scripts/tests/addon-list-pending-uninstall.test.mjs

@@ -0,0 +1,83 @@
+// Run against the addon-list.mjs extracted from the patched Firefox omni.ja:
+// node app/scripts/tests/addon-list-pending-uninstall.test.mjs <path>
+import { readFileSync } from 'node:fs';
+import { runInNewContext } from 'node:vm';
+import assert from 'node:assert/strict';
+import { test } from 'node:test';
+
+const sourcePath = process.argv.at(-1);
+if (!sourcePath?.endsWith('addon-list.mjs')) {
+	throw new Error('Pass the patched addon-list.mjs path as the last argument');
+}
+const source = readFileSync(sourcePath, 'utf8')
+	.replace(/^import \{[\s\S]*?\} from "\.\.\/aboutaddons-utils\.mjs";\s*/mu, '')
+	.replace('export class AddonList', 'class AddonList')
+	.replace('customElements.define("addon-list", AddonList);', 'globalThis.AddonList = AddonList;');
+
+function createList(currentById) {
+	const context = {
+		HTMLElement: class {},
+		ChromeUtils: {
+			importESModule: () => ({ AddonManager: {
+				getAddonByID: id => typeof currentById === 'function'
+					? currentById(id) : Promise.resolve(currentById.get(id)),
+			} }),
+			defineESModuleGetters: () => {},
+		},
+		isPending: addon => addon.pendingUninstall,
+	};
+	runInNewContext(source, context, { filename: sourcePath });
+	const list = new context.AddonList();
+	list.removeListener = () => {};
+	list.updateAddon = () => {};
+	list.removePendingUninstallBar = () => {};
+	return list;
+}
+
+test('a replacement clears the pending removal and survives list teardown', async () => {
+	let uninstalls = 0;
+	const old = { id: 'plugin@test', pendingUninstall: true, uninstall: () => uninstalls++ };
+	const replacement = { id: old.id, pendingUninstall: false };
+	const list = createList(new Map([[old.id, replacement]]));
+	list.pendingUninstallAddons.add(old);
+	list.onInstalled(replacement);
+	assert.equal(list.pendingUninstallAddons.size, 0);
+	await list.disconnectedCallback();
+	assert.equal(uninstalls, 0);
+});
+
+test('list teardown checks the live add-on even before the install event arrives', async () => {
+	let uninstalls = 0;
+	const old = { id: 'plugin@test', pendingUninstall: true, uninstall: () => uninstalls++ };
+	const replacement = { id: old.id, pendingUninstall: false };
+	const list = createList(new Map([[old.id, replacement]]));
+	list.pendingUninstallAddons.add(old);
+	await list.disconnectedCallback();
+	assert.equal(uninstalls, 0);
+});
+
+test('a genuinely pending removal still finalizes', async () => {
+	let uninstalls = 0;
+	const old = { id: 'plugin@test', pendingUninstall: true, uninstall: () => uninstalls++ };
+	const list = createList(new Map([[old.id, old]]));
+	list.pendingUninstallAddons.add(old);
+	await list.disconnectedCallback();
+	assert.equal(uninstalls, 1);
+});
+
+test('a reconnect during lookup leaves newly queued removals intact', async () => {
+	let resolveLookup;
+	let uninstalls = 0;
+	const old = { id: 'old@test', pendingUninstall: true, uninstall: () => uninstalls++ };
+	const fresh = { id: 'fresh@test', pendingUninstall: true };
+	const list = createList(() => new Promise(resolve => { resolveLookup = resolve; }));
+	list.pendingUninstallAddons.add(old);
+	const teardown = list.disconnectedCallback();
+	assert.equal(list.pendingUninstallAddons.size, 0);
+	list.isConnected = true;
+	list.pendingUninstallAddons.add(fresh);
+	resolveLookup(old);
+	await teardown;
+	assert.equal(uninstalls, 0);
+	assert.equal(list.pendingUninstallAddons.has(fresh), true);
+});