If you are reading this blog, you are probably like me in that you downloaded a 10.x update to Firefox and found that OBIEE no longer works. Here is a quick and dirty workaround until Oracle is ready with a patch:
1. type "about:config" into an address bar
2. right click anywhere and choose New / String
3. name it "general.useragent.override"
4. put the value "Mozilla/5.0 (Windows; Windows NT 6.1; rv:10.0)Gecko/20100101 Firefox/9.0"
5. refresh OBIEE login screen
