Boomerang — install on this computer

One-time per computer (work + home). After this it auto-updates — you never reinstall on a fix.

1. Make sure Tampermonkey is installed (free): get it here.
2. Click to install the script — Tampermonkey opens an install page, hit Install:
   Install Boomerang
3. If you previously loaded the unpacked extension, remove it at brave://extensions (so you don't run two copies).
4. Open Gmail and refresh. A blue Boomerang panel appears bottom-right.

Works on all your inboxes. Buttons apply the Boomerang/* labels; the engine runs on the server 24/7. Every fix I push auto-updates here within a few hours — no reinstalling.