I still use it today because usability wise it's just better for me.
I can't for the life of me get used to a separate search box. The "omnibar" is simply fantastic. Coupled with turning off "search suggestions" in the Settings, you have a wiki on hand pretty much. Anything you type will match a personal bookmark, or a personal search. Or title of a page visited earlier. This means I don't need to make bookmark in many cases. I can also manage omnibar to give optimal results by making random, useless searches in a private window, which again, is so easy to use in Google Chrome (Ctrl Shift N). And then if a search match is inconvenient for speed or just not useful anymore, just shift+del to remove it.
Firefox completelty lost me when I looked back and it was like version "52" instead of the version 14 or something I was one, just a year or two later. I was like "what the hell??" "WOW what are all these amazings updates they made?" Only to realize barely anything changed at all.
And lately they just lost me completely as a developer. They wanted to integrate the Firebug extension, arguably the most useful aspect of Firefox for developers. I kept using Firefox for firebug for years, while Chrome was my main browser. But since they integrated it, it just performs worse. It's so damn slow and unusable, meanwhile Google console just gets better and better.