Firefox - https://addons.mozilla.org/en-US/firefox/addon/ai-chat-context-window/

Chrome - https://chromewebstore.google.com/detail/ai-chat-context-window/mimifpjpnpkpkkjbmkpchgdglkdmdmof

Github - https://github.com/quantum-pilot/ai-chat-context

I think these companies should display how much tokens have been used for a model in chat (especially paid plans), but I guess they don't because it probably backfires on them.