Gemini works, but ChatGPT is broken. I never used (and won't use anymore due to ethical issues) other mainstream platforms, so I can't say anything about them.
Btw, to save full chat, you have to scroll all the way up in Gemini, until it loads everything.

It still doesn't work on Grok.com! so for now 3 instead of 5.
Please fix it! It's the best extension for exporting chats, but it needs fixing.

It does work with ChatGPT and Gemini, but refuses to work with Grok (only saying "Please go to the chat page"). The Chrome version works correctly, so maybe it's not properly tested with Firefox.