Everybody says the new Firefox is fast, but when I load up sites on my computer it's not faster than the old Firefox was, and definitely not faster than any other browser I can run on the same hardware. The initial load feels fast, but it feels like they're throttling JS events or something - anything that listens to events to do anything related to CSS brings the browser to a crawl!
This week I spoke to Firefox developers and they said I found a regression (yay me) and 2 bug reports were filed. It seems perhaps they do something 2x as often as they need to during the processing of CSS, and for some people there's little difference, but for me for example pages that get 40-50 FPS (rendered frames per second) in Chrome will get 1-2 FPS in the new Firefox, like running at 1/25th-1/50th the performance of other browsers.
Hopefully they can fix this, Firefox is the only browser I have to lose work time trying to help them file report bugs for.