That's absolutely not normal. Our site uses under 20MB for each page load (and we have the JFBCFan module showing on some pages). Your error is indicating you're going past 256MB!
Can you tell me the following:
* Does this error only happen when enabling the JFBCFan module and it goes away when not there?
* If you switch the template to something else and test, does the error still happen with the JFBCFan module?
I'm honestly stumped right now. We've never heard of this and the JFBCFan module is very 'light' in the scheme of things. There's no reason it should be doing that. Martin is definitely correct that that is not normal.. at all