Today I upgraded WordPress to 3.6. As usual, the upgrade was fast and without any problems… except that the Visual Editor stopped working :-(. From a short internet search it seems that I am not the only case.
So I followed the troubleshooting guide, refreshed my browser cache, changed computers, disabled all plugins, and voila! works. After enabling each plugin one by one and trying the editor I found that the Jetpack plugin was guilty – it seems to cause a problem in the visual editor’s toolbar which then makes the whole text in the editor white :-(. I tried many things but nothing worked, until I found this troubleshooting guide which also says “flushing any caching plugins you might be running, as well as server and/or browser caches“. Aha! I didn’t think of the server cache!
So I stopped and restarted my server, and voila! problem gone.