Works as advertised.

I was initially confused because there is another plugin, apparently from a different developer, with the same name. I can see how the author of the Firefox add-on used that similarity for extra exposure, which I’m fine with. It actually helped me discover this extension in the first place, so that was a smart move.

The author seems to be a developer himself, probably porting or vibe-coding a Chrome extension to Firefox. Also fine by me.

Works as expected.
Finally, I can run CGPT UI on my old PC, which has >10y old 4 crappy 4 cores CPU.

Brilliant!