Thanks for this report.
I would need more information to understand what does not work on your setup, in order to be able to fix it.
In particular I guess there might be some JS errors. If you installed this add-on on laptop, you could access those by pressing F12, going to the "Console" panel, and then navigate to x.com. It would be great if you can send me the errors that you see there, either by opening a bug report on https://github.com/gturri/ToXCancel-firefox/issues ; or by sending me those information at toxcancel@gmail.com .
If you are using this add-on on a smartphone, it may be a bit more complex to access those errors. If you're on a mobile I would be interested if you can send me information on your OS and your version of firefox.
Thanks!