It's made me reduce the amount of features I use in Firefox because I feel I can't trust the features will be there anymore or work the same in the next release.
Often the benefits are small, and the changes seem to be for the sake of changing things rather than to bring tangible improvements.
Workflow-breaking changes are incredibly frustrating for the user, and something a mature project should only do with extreme reluctance. Yet Firefox seems to do it haphazardly.
I would honestly be happy to use a browser that looked and worked like Netscape 1.0 as long as it supported modern web standards and didn't keep moving buttons around.