I started using it pretty much from the beginning and have never had a reason to stop. When Chrome came along, I thought the whole idea of using a browser made by Google was obviously awful, so I just kept using Firefox. And I'm still using it.
There were a few moments where Firefox seemed to stumble a bit and I did give Chrome a try. Otherwise, Firefox has been my primary browser for ages. Even to the point where I was using a portable version on a locked down computer ages ago. It just works and it respects me as a user.