All I know there is a serious bug in v. 3.6 that applies to forms (like when I submit a form the post does not execute). It happened here on WW too among other respectable sites, hopefully they will fix it.
I saw this happen to my mother-in-law the other day on a emailing website she uses all the time, but she was running FF3.5.7. The next day I upgraded her to FF3.6 and the problem went away. I'm currently using FF3.6 here on Webmaster World with no problems.
[edited by: tedster at 12:53 am (utc) on Jan. 26, 2010]