There is one,infact they are planning to switch to a more chrome like dev cycle.
As seen here -http://arstechnica.com/open-source/news/2011/03/mozilla-outlines-16-week-firefox-development-cycle.ars you can also find news on it at about any technology news site.
Chrome, Safari and Opera all pose complications for developers as it does now handle javascript the same causing many web apps to not function correctly. Once they make them more developer friendly they may take over the top spots but not until then.
The main reason FF is slow for people is they load it up with addons. I had noticed my Firefox getting slow so I uninstalled all the addons. Once again it was fast and smooth. You should only use the addons you really feel you need.
I had to switch from my preferred FF v3.6 to FF4 since my computer suddenly got incredibly slow on Sunday. Much better now, speedwise. Otherwise...I wouldn't like it.