Pbroc

(Firefox 86.0.1) I have the "block videos between " enabled, don't know if it's related.

I ditch Firefox for Edge in the meantime, everything work fine now.

(By adding I mean, blocking based on words independently of the font, to be clear)

Too bad, I guess the best would be letting YouTube deal with it, but like you said, if foreign languages use it, we're screwed then.