For me, the URL bar change is annoying, but it's the lack of customisation that's due to follow which is the problem. This story illustrates one of the reasons why. This happened to me yesterday (paraphrasing for simplicity):

Dad walks into my room, who is NOT a power user and only uses Firefox on my recommendation and says 'Firefox has changed, something weird with the address bar and it's annoying'

I respond, 'Yes, it's changed in a new update'

Dad says, 'Oh. That's a pain. How do I change it back?'

I say, 'you can't in the options at the moment - there is a more complex way but they're not going to let you do that more hidden way soon either'

Dad says 'oh ok. Guess we should change it with the harder way and just not update in future then. I don't want to change browsers it's got loads of bookmarks and settings in I like'

Me, 'you can't just not update - it'll cause all kinds of problems'

Dad says, 'well that's stupid. I thought Firefox was good because it allowed you to customise things? Oh well doesn't matter - I might go back to using chrome or the Microsoft one. They're simple at least. Just, not a fan of Google using everything but at least it's simple'

And so another user walks away from Firefox. What Mozilla aren't recognising here is that the non-power user won't try and stand up for their product. They'll just walk away to the easiest alternative. My dad's already started moving bookmarks etc over to chrome now because of this simple change in the update. I'm not sure he'll come back to firefox now

There will be others, and the market share and support will only get smaller if customisation is removed. I'm on the fence myself about jumping ship elsewhere and have been a Firefox user for longer than I can remember.

Mozilla - for your own good, satisfy your die hard fans and listen to feedback. Other users will follow but lose the core user base and you will have no foundation on which to stand. The masses will just go after the easy option (chrome) if there's even the slightest bit if resistance to the browsing experience.