Reorganize Firefox configuration and repository documentation

- Configure Firefox with privacy settings and extensions (Bitwarden, Plasma Integration, MetaMask, Kagi Search, uBlock Origin)
- Set Kagi as default/only search engine
- Add MOZ_USE_XINPUT2=1 for smooth scrolling
- Create context/ directory for concise unit documentation
- Create tests/ directory for test scripts
- Move test-firefox-config.sh to tests/
- Update agents.md with documentation workflow guidelines
- Fix syntax errors in desktop.nix and dev.nix

context/firefox-extension-update-2026-02-16.md

@@ -0,0 +1,33 @@
+# Firefox Extension Update - 2026-02-16
+
+## Changes
+
+### Removed
+- Privacy Badger (`jid1-MnnxcxisBPnSXQ@jetpack`)
+- Facebook Container (`@contain-facebook`)
+- Multi-account Containers (`@testpilot-containers`)
+
+### Added
+- Bitwarden (`{446900e4-71c2-419f-a6a7-df9c2b2dc922}`)
+- Plasma Integration (`plasma-browser-integration@kde.org`)
+- MetaMask (`webextension@metamask.io`)
+- Kagi Search (`kagi-search@kagi.com`)
+
+### Kept
+- uBlock Origin (`uBlock0@raymondhill.net`)
+
+## Search Engine
+- **Default:** Changed from DuckDuckGo to Kagi
+- **Alternatives:** All removed (Google, Bing, Yahoo, etc.)
+
+## Build
+```bash
+nixos-rebuild build --flake .#framework
+sudo nixos-rebuild switch --flake .
+```
+
+## Manual Setup
+Sign in after first launch:
+- Bitwarden account
+- MetaMask wallet
+- Kagi account (for full search features)