Hello Barb.

Although possibly not related to your problem, I have to remind you that the version of Firefox you are using at the moment has been discontinued and is no longer supported. On top of this, it has known unpatched bugs and security problems. I urge you to update to the latest version of Firefox, for maximum security, stability, performance and usability. You can get it for free, as always, at getfirefox.com.

As for your question, hopefully this support article is what you need:

http://support.mozilla.com/en-US/kb/Pop-up+blocker

if you want to block porn use either opendns familyshield or k9 web protection,both are free: http://www.opendns.com/familyshield http://www1.k9webprotection.com/