Thunderbird addon guidelines/policy/standards?

So I’ve installed an addon called “quickfilters” which is quite good, but it puts a banner across the whole TB window with a flashing “buy license” button … is there any policy on which addons will be allowed in TB, which will be promoted in the addon repos, etc.??

This is not fine with me, I expected|expect some sort of standard for addons that are available direct from the mozilla repos.

Is there any official policy against such things? If not why not? And if so where can I report it?

Thanks - note that the banner is in place on all screens, not just the addon screen, and the buy license button flashes (I mean, for real!).

FWIW the source is supposedly available, so I guess I can fork it for myself, but it’s 504’ing (“Gateway Timeout”) on the site, .