David,
The cache is a list of files that Netscape (or whatever browser you use) stores on the computer so that if you go to a site regularly it can load the pages quickly, or when you change the page and go back it can load from the stored files on the system rather than bring them all down from the site again (yes, even those naughty ones leave a mark). The browser does this regularly to keep the files fresh and the more sites you visit the more files are stored and the longer it can take to get pages loaded. You can flush this out and free up room by removing files from old sites you went to but never returned to and refresh the files when you go back to a regular site.
Rob,
I had a problem a while ago (not with F.M. but my ISP) they changed the layout and one day when the updated site went live, I couldn't get access to it. When I contacted them they said I could try a new browser which I did and it worked, I used to use Communicator but now use Navigator, could it be something like this?