I don't know if you're willing to consider it evidence, but I think Apple's success is in large part due to their software and their UI's. iOs in particular.
Also, user interfaces might be closer to fashion than you would think! If you consider Windows XP's look. Imagine Windows 10 looking like that. Or consider Windows 8's different looks compared to Windows 7's. Or Google "material design" on Android Lollipop. Dang, this is exactly like fashion! :D
But other people felt the look was dated, and well over-due for a refresh. I guess the Firefox developers were in that group.