Undeniable fact: you have experienced the issue when your stat graph box didn't load.
I just checked it and it worked fine for me. So there might be that this problem is not occurring anymore. You said you cleared the cache so you probably refreshed it as well and the graph still kept missing.
You should try that on the other computer and/or browser. If it's fine, then the problem is with your Firefox. If it happens for you on any other pc/browser, then this is the issue that is strictly related with you. In this case you would be checked for problems and those problems would be removed eventually.