Edit 3: it happened again this morning (Jul 7, 2013): slow TeX rendering in short answers. But everything is fine again now...
Edit 2: I have just tried to edit the same answer again on the same computer and with the same browser. It is still a bit slower than for short answers, but only a tiny little bit. Everything is fine now...Note that I did not restart, nor reboot anything (computer/browser) in between.
Edit: as indicated, by @ˈjuː.zɚ79365, the reason seems to be that I was editing a fairly long answer, in which case a solution is to work on it elsewhere. I have edited long answers without a problem before, and I have encountered the problem before on short answers. So I guess I'll leave the question open.
My computer is a 2009 iMAC, operated by Mac OS X Lion 10.7.5 with processor 2,66 GHz Intel Core 2 Duo. My browser is Chrome Version 27.0.1453.93.
I am aware of that thread which asked the same question in 2011. But we are in 2013, so I guess the website has technically evolved a bit in between. So maybe there are new reasons.
I have just added a 5 line paragraph to an answer on the main site. It took me about 45 minutes...The answer box was essentially frozen the whole time. I would type a few characters which would appear about 30 seconds later... Here on meta everything works normally.
It happened before, not so often I must say, when I was using different operating systems and different internet connections.
I am not complaining, I find that MSE works remarkably well in general. I am just curious about what causes this: heavy traffic, maintenance, just my system...? How long should I wait on average to make sure everything works well when I come back?
I have read the answers on the similar questions, so maybe I'll try these bookmarks to disable rendering: see robjohn's answer. But I could not find answers to the two questions I ask in the previous paragraph.