I have used Mozilla Firefox as my main browser for a long time now.
It is a fundamental part of the web & provides the only real alternative to browsers based on the Google Blink engine.

There are various posts on this site regarding scripts I've written for Firefox both on Linux & on Windows but recent changes have lead me to stop using Firefox completely.

updated Oct 8 2021 added information regarding Firefox Suggest

Negative Changes #

The most recent change which made me question whether to continue to try to fix things was the GUI.

Mozilla released a update which made tabs look like webapp buttons.

Then last week they released version 92.0 changing bookmarks dropdown menus to be huge adding padding & rounded corners.

I personally don't expect desktop applications to look like someones first time using CSS.

Over time I've built up a userChrome.css to fix a lot of changes but as time goes on & Mozilla diverge away from desktop app design I start to question if it's even worth it.

I also have a custom prefs.js disabling many builtin features of Firefox.

Forced Features #

There are various features which seem to have been added & have become enabled by default in Firefox.

DoH #

This can be detrimental to many users depending on how their network is setup as it bypasses the nameserver set by the network.
This can lead to DNS lookup problems & bypasses any blocking people may have setup (eg: many use dnsmasq with pihole to block adverts & tracking).

There's also the view that forcing users to use a single nameservice creates a central point for monitoring & analytics.

Pocket #

This is a small thing but it should not be forced onto users.

In addition a default install also has Pocket Recommendations (Adverts) on new tabs (introduced in Firefox 77).

ffox_77_pocket

This feature is still active with pocket disabled.

GUI Changes #

Huge zoomed urlbar introduced in Firefox 75

firefox-75-search

Tabs that look like webapp buttons introduced in Firefox 89

Huge bookmarks dropdown with rounded corners introduced in Firefox 92

firefox-linux

Comparing the two screenshots above you can see that tabs went from square with a color accent above to show active tab to being a rounded button with no color & a smaller close button.

Mozilla Remove Compact Option #

Mozilla want to remove the compact layout in firefox & so far have removed the option from the browser, stating they will not support it.
There is a thread on bugzilla showing there are no real benefits in doing this

Bugzilla: Remove compact mode inside Density menu of customize palette

The OP does a good job of showing how bad their UX is without even realizing suggesting the customize option is 'fairly hard to discover'.

They also seem to assume the use of compact mode directly relates to desktop resolution despite not showing any reasoning or stats referencing this.

Mozilla Adds Firefox Suggest #

Mozilla have now added adverts in the address bar with Firefox Suggest (version 93.0 Oct 5 2021).

ffox_93_suggest

This feature is enabled by default meaning users need to opt out.

Mozilla Blog: Data and Firefox Suggest
Mozilla Support: Firefox Suggest

Conclusion #

Some of these things might seem small to many but a large percentage of time on the computer is spent looking at the web browser & there are many other options with better features when it comes to UX & UI design.

I question whether Mozilla see Firefox as a desktop app or a web app as it seems the more changes they make the more their web browser looks like a web app.

As a user I feel like I shouldn't be trying to fix GUI changes over and over so am now testing out alternatives like Brave.

Firefox Fixes #

I have scripts for creating profiles with fixes for most of the GUI changes & settings overrides available on github.

ffox_profile_tools

I recently added a fix for the bookmark spacing (there are still rounded corners on the dropdown so it still looks bad).