No. It was successful because of a massive business development and community building effort in addition to the product. Firefox was less compatible than IE because IE was what people built for.
Konqueror's KHTML engine was actually more feature-complete for much of the time but there was no organization backing it until Safari based early Webkit on it. And Apple didn't back KHTML so much as just base Webkit on it. Epiphany was a Webkit-based fully open browser but didn't actually get as popular as Firefox.
The whole Firefox thing was a huge success. When they turned Mozilla (the browser) into this it was a feat. And then to coordinate the complex efforts to beat IE. It was amazing stuff.
It was a really well-done job by Mozilla.