Empty filelist in FF

[yermulnik]

I'm on FF 100.0 (64-bit), but this may have started to happen much earlier as I usually use Chrome to browse GitHub issues and PRs.
The Better Pull Requests for GitHub side panel shows up for me as an empty box.
Any clue on why this is happening and how do I fix this? (no such issue in Chrome if this matters)
Here's the example:

[yermulnik]

Some factoids which may matter: I have Ghostery to fight ads which is turned off for github.com, and Greasmonkey which is turned off at all. No any other extensions which may block page contents (as of my knowledge). All the same setup for Chrome (Ghostery and some other extensions which don't mess with page contents though), where Better Pull Requests for GitHub works as expected.