I changed the timeouts from 500 to 5000 ms and it helped, but it didn't completely solve the problem.
Now that I made the change, the equation editor works with with Safari 6.2.2 and 6.0.5.
It works with Firefox 32.0.3
But not in Firefox 35.01, unless Firefox is in "safe mode".
All of these tests were done with my server under no-load conditions.
With Firefox 35.01, I tried it with all extensions and add-on deactivated, and the equation editor still doesn't work. Perhaps I will "downgrade" to an earlier version of Firefox.
Fortunately my students' computers are frozen into older versions of Firefox and Safari so I'm hoping it will OK for them.
So altogether, I think that the timeout was part of the problem but that there are other problems too, some in Firefox and maybe some in other places.
By the way, I noticed that there is a difference in the equation editor's performance depending on where it it being used. For example when I'm editing the front page of my Moodle site, the equation editor seems more robust than when I'm previewing a quiz essay question.
Thanks for the help...
PS: I did switch to MathJax, and it didn't make any difference.