I have CPF set to the highest security it allows and have no problems with any feature of this forum, or any other forum I have been to (quite a bit).
I personally suggest you scan through your application/component monitor rules and see if you can find anything that you might have denied. Also, are you using a proxy or web filter?
I have used this forum in both FireFox, and IE. If worse comes to worse, you could try deleting all of the application/component monitor rules and starting fresh (Under Security/Wizards you can run the "Scan for Known Applications wizard). Maybe try to be more carefull when creating rules... this is about all I can think of.
If you decide to get a fresh start on your CPF rules, don't foget to restart it
