I tried the beta version as well same problem. Canary doesn't do modern/immersive it seems
I wonder why google and FF complain so much about not being allowed to do RT browsers when they apparently don't care at all.
I don't suppose anyone forked the FF modern/touch build into one of the other alternative FF builds ?
Canary should allow immersive mode when Chromium can also do it.
Nope, nobody forked FF modern build, although some old build might be available in tinderbox builds although I will not recommend it using.
I think more like this issue is related to some field trail test nuking your immersive mode or Intel graphic driver messing up.