Hi KriegeR,
Welcome to the forums!
The only thing that comes to mind - there are two parts to the URL in the Account Settings...
The 'When URL Contains' field, and the 'Use This URL' field.
If you have all three 'Use This URL' fields set to the same thing for each account, then when PM generates the password, it is using the same URL *string*, even though the actual URL you are at is different.
What I generally do is put enough of the URL string to prevent phishing scams in the first, then just the base URL for the 'Use This URL' field. Example:
For the forums login here, I set them up as:
When URL Contains: //forums.passwordmaker.org/
Use This URL: passwordmaker.org
If this isn't your problem, then we'd need to know the actual URLs to try troubleshooting further...
Also - what version are you using and what version of FireFox?