Update .github/copilot-instructions.md

Co-authored-by: qodo-merge-pro[bot] <151058649+qodo-merge-pro[bot]@users.noreply.github.com>

Author: PeterDaveHello

.github/copilot-instructions.md

@@ -55,7 +55,7 @@ Since this is a browser extension with no automated tests, ALWAYS manually test
 
 1. **Load Extension in Browser:**
    - 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.
+   - 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 (unsigned) add-ons are removed on browser restart; you must reload them via the same "This Firefox" page after every restart, and some environments with enterprise policies may block loading from file.
    - **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:**