search the word "ad" or "ad block" in the ADD-ONs section , and install one of these add-ons that blocks ads , i had this problem too, once i installed this one via add-on search , 90% of the adds wont open , but like i said 90 % , not all : http://jessehakanen.net/adblockpluspopupaddon/

You have a couple of plug-ins I wouldn't let near my computer -

Widdit Mozilla Plugin

The BearShare plugin allows you to open and play tracks on BearShare

You can Google them to get the general idea of why they may be causing problems. Do you actually use them? Disable them by setting "Never activate". Does that help.