To be very precise, I use the Fennec build off of F-droid, so it may be trailing FF from the Play-store a bit. Sounds like an incident, not deteriorating quality in any case. I'm happy as a clam with FF/Fennec.
The last major redesign broke/removed "Undo Close Tab", with a promise to bring it back. I found that decision to be staggering. It's not even clear what purpose the update served, except as an example of the development approach that jwz assigned the epithet of "CADT" 15+ years ago.
I use Fennec from F-Droid as well. The redesign broke many features for me and rendered it near unusable (or actually unusable for certain tasks, like downloading files).
