I can confirm this, everyone I knew at the time was coding on Firefox even if no-one required any compatibility with it just for that reason, it was just much easier to code with.
When I shared my observations with coworkers, they would nod and say they had experienced the same thing. Same with peers I knew outside of work. Either we were in a very large bubble, or that was happening everywhere. And I think the rise of Mozilla aligns with those observations. It 'just worked' because everyone quietly made sure it did, even when people told them not to.