Try clearing the cache via Tools | Options | Advanced and click the "Network" tab. Then click the "Clear Now" button.

Also, go to Tools | Clear Recent History. Then in the panel which appears, click the "Details" arrow and checkmark "Cache". In the dropdown menu at the top, change it to "Everything" and then click "Clear Now". See the attached image for more info.

I am afraid that that didn't help. I also note that whenever I press a tab a window pops but it disappears too soon for me to read the url.

Do you have the option called "Tell web sites I don't want to be tracked" enabled in Tools | Options | Advanced?

Or do you have Ghostery, or any other kind of add-on which prevents web tracking installed?

Are you accepting cookies for Facebook and third party cookies?

You could also try running Firefox in Safe Mode. You can do that by clicking Help | Restart with Add-ons Disabled. Then click "Continue in Safe Mode" without checkmarking any of the boxes you'll see in the next dialog box.

Ah, accepting third party cookies solves the problems. Is this really necessary though???? Third party cookies are a major contributor to adware problems. I am fairly sure that I had this same setting in Firefox 3.6 and had no problems with Cityville. I hope that you can work around this problem so that we don't have to accept third party cookies in order to run Cityville.

You can try setting FF to accept session cookies instead. I use an add-on called Cookie Monster which you can install from here: Cookie Monster

That way, the cookie gets deleted at the end of your session on Facebook.

surely there must be a better way than to install yet another extension

can we try to reduce the number of needed extensions in the privacy arms race