I was including all "Mozilla" browsers (Phoenix, Firebird, whatever) under that umbrella. I didn't start using Firefox seriously until roughly 1.5. Maybe it was just me!
I was there too. Actually ever since Mozilla M1 or M2 I think. Things were pretty rough back then (so much blue!). Then the browser-only Phoenix followed by the rename.
I (and presumably others) hated the notion of a Microsoft/Windows-only web. Younger folks just don't realize how close we came and the debt owed to those Mozilla devs.
That doesn't match my memory at all, unless you include Phoenix under the Firefox umbrella. I switched … I don't remember exactly when, probably in late 2003, but certainly when it was called Phoenix, and it was such a breath of fresh air coming from IE. I'm sure there were breakages, because it was the early noughties and that's what the internet was like, but I don't remember a single time wishing for something that IE provided that Phoenix didn't.
But I was just coming to it as a user, not as a dev—maybe you're referring to the dev perspective.