A decent chunk of the users who bothered installing an adblock would also be bothered enough to install a FF fork with adblock, so I doubt the revenue increase would be much. As for calling it "off-mission": yes, what's even the point of FF if that's the route it goes on?
Do any of these forks have the ability to sync, either with Firefox or something self hosted? Or are they all just basically reskins with a single toggle added or such?
> Do any of these forks have the ability to sync, either with Firefox or something self hosted?
The Firefox Sync web service is provided by Mozilla but can be self hosted: https://github.com/mozilla-services/syncstorage-rs. That could also be used in forks. See e.g. https://librewolf.net/docs/faq/#can-i-use-firefox-sync-with-... . I don't understand what you mean by sync with Firefox.
> Or are they all just basically reskins with a single toggle added or such?
Hard to generalize, but definitely not all of them. see e.g. https://lwn.net/Articles/1012453/