However she thought it was totally fine as she was used to it :S
No, it wasn't.
Quick reminder, the issue with IE was webpages loading broken, or not loading at all.
People that used that crap didn't switch because "Chrome was a bit snappier than FF", they switched because all of a sudden every webpage, many sotfware install wizard, and even billboards on the street told them to switch to Chrome. Some "toolbars" installed it without asking. They probably never had heard of FF or Opera before.
It will be interesting to see what happens next year in that case, because FF+UBO will be much faster than Chrome with a nobbled ad blocker. If your right and speed is what everyone cares about there should be a mass migration back to Firefox.
But I doubt it, because we have already have a similar experiment. FF+UBO on Android is blazing fast compared to Chrome on Android. Chrome not supporting extensions on Android means the situation is nothing like desktop where Chrome and Firefox are roughly comparable (and always have been). On an ad laden site FF+UBO is going to load a page several times faster. More to the point to me, ads on desktop are often "out of the way" of the main content, but on mobile that consume roughly 1/3 of an already small screen. Like the ancestor poster, I'm stunned that nobody uses Firefox mobile (I'm defining 0.49% market share as nobody). Performance wise the difference is enormous - yet clearly no one cares.
Which also means, you and I and other nerds notwithstanding, it likely no one cared about Firefox's performance versus Chrome when they switched on the desktop. Marketing, bundling, breaking of Firefox on Google's home sites look to fit the facts much better.