What is really hitting Firefox hard is the lack of a viable (or at least popular) mobile browser.
As the mobile web explodes, and Mozilla is barely even competing in that market, then their overall market share will fall.
As the mobile web explodes, and Mozilla is barely even competing in that market, then their overall market share will fall.
The new Firefox Mobile, currently in beta, is quite good - it uses a native Android UI and is very fast and smooth. The older version, which used XUL, was indeed sluggish.
But, to be fair, none of this really matters. iOS and Android are by far the top mobile OSes, and hardly anyone replaces the default browser on them, which makes it extremely hard for alternative browsers (Firefox, Opera) to make any headway. Tech people like HN readers might, but 95% of people just use the default browser on their phone.
The performance cost of XUL, though, is just too much for mobile.