My memory may be failing me but I think Firefox 3 was also where it started to feel less like the snappy minimal utilitarian “just a browser” it was in versions prior and started to feel more clunky, branded, and product-y, which also didn’t help its adoption in my opinion.

If nothing else it primed users for adopting Chrome, which originally had a less branded, more utilitarian feel not unlike early Firefox.

This cycle is somewhat repeating itself though as Chrome has become very branded and product-y. Would love to see something similarly functionally-minded as early FF/Chrome come out and take a big bite out of Chrome’s marketshare.