feat(extension): add Firefox WebExtension support

- Add a neutral WebExtension API adapter that uses Firefox browser.* or Chromium chrome.* without mutating globals.
- Switch extension runtime code to the adapter and add Firefox-specific typings for tabs, windows, tab groups, storage, scripting, and native messaging ports.
- Fix Firefox temporary add-on instructions to load the packaged manifest with background.scripts instead of the Chromium service worker manifest.
- Detect Firefox in clients.list via runtime.getBrowserInfo and keep Chromium user-agent fallback support.
- Make navigate.open wait briefly for Firefox to replace initial about:blank with the requested URL.
- Add JS coverage for API selection, clients.list browser detection, and Firefox navigate.open URL polling.
- Bump package and extension version to 0.15.2.

extension/src/core/scripting.ts

@@ -1,15 +1,17 @@
-// chrome.scripting.executeScript wrapper with transient-error retry.
+import { webExtApi as api } from '../browser-api';
+import type { ScriptInjection, ScriptInjectionResult } from '../types';
+// api.scripting.executeScript wrapper with transient-error retry.
 import { isTransientScriptError } from './errors';
 import { sleep } from './throttle';
 import type { Serializable } from '../types';
 
 export async function executeScript<Args extends Serializable[], Result>(
-  options: chrome.scripting.ScriptInjection<Args, Result>,
+  options: ScriptInjection<Args>,
   retries = 3,
-): Promise<chrome.scripting.InjectionResult<chrome.scripting.Awaited<Result>>[]> {
+): Promise<ScriptInjectionResult<Result>[]> {
   for (let i = 0; i < retries; i++) {
     try {
-      return await chrome.scripting.executeScript(options);
+      return await api.scripting.executeScript(options);
     } catch (e) {
       if (i < retries - 1 && isTransientScriptError(e)) {
         await sleep(300);