Mull Browser != Mullvad Browser
I have been using mull browser for around 1 week now. I felt like mull browser is funtastic without those firefox garbages. Also the tracker blocking is at maximum. Usually firefox have strong tracking protection than any other browser like brave, vivaldi, edge, etc. None of my usual visiting webites got blocked/breaked at all.
I only have to use localcdn and ublock origin in this browser. It's faster than official firefox but lesser than chromium but it's ok.
Ghecko based browsers. Its due to sandboxing issues on mobile. Desktop is fine.
Edit: I don't know why your getting downvoted when what your saying is vague but true. Guess others want sources instead of they, and detailed info about the actual issue. It is simply a site isolation and sandboxing issue nothing more that I am aware of.