For the purposes of this comment, user-hostility means decisions that have negative utility for Firefox users as a whole, while benefiting Mozilla in some way (usually financial).

* There is disgusting clickbait and spam on the new tab page by default, thanks to bundling Pocket's article recommendations. Many of these are sponsored suggestions (a euphemism that means "advertisement"), but ironically these are scarcely more annoying than the actual suggestions.

* The top sites feature on the new tab page, intended to provide easy access to the sites you use the most, is now infested with sponsored recommendations like Amazon and Ebay.

* The URL bar is now infested with sponsored suggestions, even if you have searching from that bar turned off!

* The have made major blunders in their handling of "experiments" and telemetry. They broke all extensions because they failed to update a certificate (after shipping Firefox with a signing requirement for extensions that can't be disabled), and shipped an extension directly to users via their hotpatching feature that implemented a sponsored tie-in with a TV SHOW which manipulated the text on web pages, a major breach of trust in their use of hotpatching.

More minor or borderline cases:

* They have shipped many of these anti-features and stuff that belongs in user-installable extensions as part of the source code of Firefox itself. This bloats the browser, makes it harder for potential forkers to remove the code, and makes it harder for them to reverse course in the future should they decide to undo their disastrous series of decisions.

* They default to Google as a search engine because Google pays them lots of money, not because they believe that's the best search engine for their users to use. They were using Yahoo a few years ago.

* They generate pointless UI churn, presumably because their design team has nothing else to do. Most of these features have been received poorly by the majority of Firefox users invested enough to speak out, suggesting that they have some other motive than making their users happy.

* Needless removal of features that arguably do belong in a browser: detection of RSS feeds, compact mode for the GUI, the ability to use CSS to restyle the browser interface (now hidden behind a "deprecated" toggle)

* On top of everything else, the horrible communication from Mozilla has made everything so much more hostile than it already was. They outright denied at first, for example, that the "new tab suggestions intended to improve the user experience" were advertisements.

* The mobile transition has been a disaster. They've had like 4 or 5 different "editions" of Firefox over the last few years as they tried to decide what their strategy was, and now that they've set on one, they deprecated the only version of their browser that supported add-ons on mobile without a replacement, and now almost 30 versions later the overwhelming majority of addons are still not supported. And the justification for all this, refactoring to make the browser faster, didn't materialize. I tested both the old and newest browser on objective benchmarks and saw a difference of less than 10%, and the UI of the new browser was noticeably slower.