Just to make sure, we are talking about Vivaldi on Android, correct?

Seeing Vivaldi’s feature bloat if a bottom bar with infrequently used buttons that blocks viewing space

What buttons do you mean? The only two buttons that I see added from Firefox are the history and the adblocker control. Both pretty useful. I also don’t see how they block viewing space. What else do you want to view in the bottom bar?

and a completely unnecessary tab bar on mobile that wastes space

… that can be turned off if you don’t like it. Also it’s an absolute killer feature and one of the main reasons why I chose Vivaldi over FF. If you don’t like it, you can turn it off. I much rather have the option to enable/disable a function than to not have the function at all.

I tried Vivaldi, don’t really even see a difference between the tab drawers.

Try to drag-and-drop a tab. In Vivaldi, it works exactly as expected.

On FF it first goes into the multiselection mode and only if you drag it over its stubbornly clingy dead zone can you rip it from its position. ~1/4 of the time the whole screen jumps to a random position, especially if you have many tabs. If you drag too early, the tab doesn’t get moved at all, but instead the whole screen moves.

Other than that, I see that they fixed some of the jankiness that it had a year ago when I last seriously used FF on Android.

when these single press buttons can easily be moved to gestures or condensed. You know, like modern UX design.

Gestures are one of the dumbest UX decisions possible, because they lack affordability in most cases. Stuff like swipe to reload/go back/go forward is pretty dumb because you trigger it accidentally a lot.

Like a third of my screen is just gone because of of redundant buttons and UI. Reminds me of Internet Explorer days with Yahoo toolbar.

What kind of screen size do you have? On my screen, the bottom bar and the tab row take up maybe 5% of the screen real estate. And again, if you don’t like it, disable the tab bar and make the bottom bar auto-hide.