I never ran into problems except with this latest version: 3.0.3

The problem: Websites with self-signed certificate are no longer working. It doesn’t give me the option to add exceptions like it used to be. (websites with exceptions added in previous versions are not effected.)

Tried this:
Go to Tools -> Option menu, select Advanced, on Encription tab click on View Certificates.
Go to Servers tab in Certificate Manager, click on Add Exception
Enter the host (https://localhost) then click on Get Certificate button.
Same problem

After some searching, some are saying to re-set one of Firefox settings in about:config. However it doesn’t work in my case.

I gave it another try in the Certification Manager by use the host name with port number. It worked!

I am glad it worked out and I don’t need to go back to 3.0.2 or wait for fix in the next version.