Well, the changes to the UI starting with Firefox 4 made it much less productive to use. Maybe they didn't realize it at the time, but the toolbars, traditional menu bar and status bar provided a lot of useful functionality. Getting rid of them, or at best forcing the use of extensions or reconfiguration to bring back such functionality, hurt the usefulness of Firefox. The minute gain in space for displaying the web page has not been worth the loss of usability.
Then there are the performance issues. They remain to this day. We constantly hear from Firefox advocates that it doesn't have poor performance, or that it doesn't use excessive memory. Yet somehow the release notes for each major release talk about "fixing" such problems.
At some point, one just gets tired of being strung along. The alternatives aren't necessarily perfect, but at least they're better in some way. If Firefox is going to try to look and behave like Chrome, yet have far inferior performance and consume more memory, we might as well just use Chrome.
You don't need extensions to bring back the menu bar, you can just enable it from the view menu.
I don't really know what to say about the performance issues though, as I don't have any. Also, Firefox uses far less RAM than Chrome on my PC. I don't understand why people worry about RAM use so much anyway. If it's not it use, it might as well not be there.
Then there are the performance issues. They remain to this day. We constantly hear from Firefox advocates that it doesn't have poor performance, or that it doesn't use excessive memory. Yet somehow the release notes for each major release talk about "fixing" such problems.
At some point, one just gets tired of being strung along. The alternatives aren't necessarily perfect, but at least they're better in some way. If Firefox is going to try to look and behave like Chrome, yet have far inferior performance and consume more memory, we might as well just use Chrome.