Problems Editing Modules After Upgrade to Joomla 3.6.3

After upgrading to Joomla 3.6.3, I ran into a problem where I could not edit a module–any module. Nor could I create a new module. I tried changing editors, but that made no difference. By happenstance, on the console I noticed that a couple of articles were locked and went to unlock them. Suddenly, everything worked normally.

Firefox Problems

I got things working on one site with the fix above, but two sites still had the same error. Using Chrome instead of Firefox bypassed this problem. I then went into Firefox and disabled all extensions: this fixed the problem as well. I’m in the process of figuring out which extensions cause the problem.s