If you come across an issue where you are trying to login to Gliffy in Firefox and you keep getting a spinning wheel that never loads, this may be due to a Flashblock plugin installed in Firefox.
You may see this screen first:
Clicking on the play button will bring you to Gliffy, but you may encounter a spinning wheel:
This is happening due to the Flashblock plugin preventing the Flash interface of Gliffy to load.
You can determine if you have one of these installed in Firefox by going to Tools->Add Ons (Ctrl+Shift+A) which will open up the Add-On Manager.
If you have Flashblock installed:
Select Options->Whitelist, then enter www.gliffy.com and click "Add" to add Gliffy to your exceptions list. Gliffy should now load in your Firefox browser.