Hmm, I don't think many have requested we sync user{Chrome,Content}.css. It's possible we'd accept a patch to sync them (I'd be for it, at least), but it's not trivial since we don't already have file syncing code.
Syncing them with dropbox and symlinking does sound to me to be the most reasonable.
Glad you're satisfied other than that!
And userChrome/Content.css... looks like I’ll need to dropbox those.
Editing css was essential to make the switch from Vivaldi to FF - yesterday! Getting TreestyleTab et al. to feel like Vivaldi with vertical tabs required some fiddling: sidebar without menu, hidden top tabs, darker text color, etc.
In any case, it’s my new daily driver and I'm quite satisfied so far. Even set DDG as the default while at it.