Firewall blocking website registration?

Hi, I’m using Comodo Internet security premium with latest updates, product Ver 6.1.275152.2801 DB Ver 16030 and I’m having problems with some websites taking a long time to open pages and when trying to submit registration on a site it timed out and I could not register.

I have found that if I go to “stealth ports” and use “alert incoming connections” this solves the problem and the website now loads quickly and I can register but why is this happening, I have not changed any settings from default when installing comodo and updating so this is happening with default settings.

I’m using firefox 20.0.0 and Adblock plus but disabling adblock makes no difference but using “alert incoming connections” does, the website I was trying to register on is Argos.uk so it’s not some dodgy site.
Thanks for any help.

Did you get alerts for incoming connections when navigating the mentioned web sites?

I'm using firefox 20.0.0 and Adblock plus but disabling adblock makes no difference but using "alert incoming connections" does, the website I was trying to register on is Argos.uk so it's not some dodgy site. Thanks for any help.
Problems with web sites are usually a problem with the browser. Try cleaning cache and cookies and restarting Firefox.

Do the problems also occur with other browsers?