I have a 400 LOC userChrome.css file because the new redesign was barely usable since Firefox beta received this makeover.
- There is no tab contrast, and very difficult to tell tabs apart. Made worse on sides without Favicons.
- I loved the mic/speaker icon when a tab is playing/listening audio. They had to make it TWO lines in the tab, and made it difficult to notice when you have more tabs.
- I could use some icons in the right top menu. It looks nice and easier to use in Edge, that has icons for every option.
- Compact mode is gone, that was discussed here before.
That said, I like the native elements (buttons, up/down arrows, etc). The new icons in the addressbar look nicer and fits nicely in.