I was able to fix the problem by using the following recommendations mentioned above:
1. Install “use Google Libraries” plugin.
2. Activate “Twenty Eleven” Theme.
3. Clear browser cache.
4. try the tabs, and everything worked.
5. Switch back to my usual theme, everything still worked!
I hope this helps.
I’m having the same issue after upgrading to ver3.3 (upgrading both code and database). After switching from the Visual tab within the post editor to the HTML tab, I can no longer switch back to the visual tab.
I’ll try the above recommendations and let you all know if I find anything that works.
