(1) In a new tab, type or paste about:config in the address bar and press Enter/Return. Click the button promising to be careful.
(2) In the search box above the list, type or paste plug*ht and pause while the list is filtered
(3) Double-click the plugins.http_https_only preference to switch the value from true to false"
After that you should be able to drag and drop the swf file into a new tab in Firefox and enjoy. You're welcome.