Hi I also had this really annoying issue. i am assuming it is due to some add-on for online games such as face book games etc. there are 2 ways to fix it and get back on firefox: 1 - reset your clock setting to a date earlier than when it says the certificate has expired (worked for me) 2 - hold down shift when opening firefox, when the pop up option box opens, check off that you want to 'disable all add-ons' it will then open with an option page for you to enable add-ons, i just went through the list and enabled an that were obviously trusted add-ons such as java, adobe etc. this has also worked for me but i have 2 add-ons that are still disabled and i dont know what they are for! guess i will find out soon if i need them tho :)

Jan