Loading of styles through load.php does not finish, the loading keeps spinning until it finally fails. There are four files failing to load, but strangely enough the defined style seems to be available.
Screen cap from Cort Adeler
Screen cap from Firefox 41.0.2
Later on checked the same load problem on Win10 running in VirtualBox on the same computer, and also running Firefox 41.0.2, and it didn't have the problem.
(Offender causing the problem is FoxyProxy, but I can't see why)