Mozilla has made significant UI changes every 3-4 years, with the last one being in 2021. Perhaps we're about due to see another?
You can feel the seething rage of current Mozilla designers for us wanting to turn off "grandparent mode" esque proportions when you see that the "compact" density is the only one that says "not supported" next to it, meanwhile the even more hilariously oversized Touch setting is totally ok.
Now if only 1Password would make it so they’re extension worked properly it.
Mozzarella has so much potential I don't want to see it wasted (again).
UI fiddling is what you do when out of ideas.
And I suspect designers like to redesign everything for the same reasons that developers prefer to implement new shiny features.
From my experience (as a user) these two contradict each other. (see Google and Microsoft products for examples).