This.
I used Firefox since back when it was known as Phoenix. It was my primary browser for many years, but I ended up dropping it back when they launched the "Australis" makeover. I didn't like the look of it as it was too similar to Chrome, but my biggest beef was just how much customisability they removed. That's been one of my constant criticisms ever since.
Firefox's USP used to be the flexibility and customisability that it had. Sadly, Mozilla seems to be determined to remove as much of this as possible, and hence for me one of the biggest reasons to use it has been steadily eroded. These days I typically use Pale Moon for most things (a Firefox fork that retains much of the customisability Mozilla removed), with Vivaldi being used for certain sites that don't play well with Pale Moon.
From time to time, I do try Firefox again, but it just doesn't have enough to tempt me back. Maybe this may change? I hope so as the web does need none-Chromium browsers.