Improve extension loading and cross-platform cleanup instructions

Co-authored-by: PeterDaveHello <[email protected]>

Author: Copilot

.github/copilot-instructions.md

@@ -54,9 +54,9 @@ Production build creates multiple variants in `build/` directory:
 Since this is a browser extension with no automated tests, ALWAYS manually test functionality:
 
 1. **Load Extension in Browser:**
-   - Chrome: Go to `chrome://extensions/`, enable Developer Mode, click "Load unpacked", select `build/chromium/`
-   - Firefox: Go to `about:debugging#/runtime/this-firefox`, click "Load Temporary Add-on", then choose the built add-on by selecting the generated `.xpi` file. If loading from an unpacked build is required, choose the `manifest.json` inside `build/firefox/` (do not select the folder directly). Note: Temporary add-ons are removed on browser restart.
-   - **Important**: Extension files cannot be tested by serving them via HTTP server - they must be loaded as a proper browser extension
+   - Chrome: Go to `chrome://extensions/`, enable Developer Mode, click "Load unpacked", then select the folder `build/chromium/` (the folder must contain `manifest.json`).
+   - Firefox: Go to `about:debugging#/runtime/this-firefox`, click "Load Temporary Add-on", then choose the generated `.xpi` file from `build/` (recommended). To load unpacked instead, select the `manifest.json` file inside `build/firefox/` (do not select the folder directly). Note: Temporary add-ons are removed on browser restart.
+   - **Important**: Extension files cannot be tested by serving them via HTTP server — they must be loaded as a proper browser extension.
 
 2. **Core Functionality Tests:**
    - Press `Ctrl+B` (Windows/Linux) or `⌘+B` (macOS) to open the chat dialog on any webpage
@@ -166,7 +166,9 @@ The extension supports multiple AI providers:
 
 ### Build Issues
 
-- Build failures: Check Node.js version (requires Node 20+), clear caches (`rm -rf node_modules && npm ci`) and build caches (`rm -rf node_modules/.cache build/ dist/`)
+- Build failures: Check Node.js version (requires Node 20+), clear caches and rebuild.
+  - macOS/Linux: `rm -rf node_modules && npm ci && rm -rf node_modules/.cache build/ dist/`
+  - Windows (PowerShell): `Remove-Item -Recurse -Force node_modules, build, dist; if (Test-Path node_modules\.cache) { Remove-Item -Recurse -Force node_modules\.cache }; npm ci`
 - Safari build fails: Ensure macOS with Xcode installed
 - "Module not found" errors: Usually indicate missing `npm ci`