I used to default to Firefox for work. Then they killed the old addons, which broke a major part of my workflow (FireFTP's "open a file and as you edit it it automatically re-uploads" feature). So there was a lot less keeping me stuck to it. Recently, and this is past Quantum, performance on some things (Google Apps) became abysmal (now, this could well be Google being half-assed or deliberately malicious about testing) but that was enough that I gave up on Firefox for work.