If we render stuff with the same technologies that websites use, it means performance improvements and bugs that affect the web affect the Firefox UI and vice versa.
It also means a UI that's noticeably slower than actual native UI. There's plenty of reasons why I use Firefox instead of other browsers, but the increased UI latency is definitely noticeable and one of the reasons why others might not want to switch to FF.
It also means a UI that's noticeably slower than actual native UI. There's plenty of reasons why I use Firefox instead of other browsers, but the increased UI latency is definitely noticeable and one of the reasons why others might not want to switch to FF.