Yesterday evening there were two posts in Meta - here, and here - concerning display problems. Simultaneously, on the main MSE site, I was noticing that comments containing MathJax could no longer be read. The details of the problems reported in the two Meta posts were different (i.e. they were different from each other, I think, and they were certainly different from the problem I was having), and no-one else mentioned, even in passing, that they were having any difficulty in viewing comments. Nor has there been any mention today of the problems that were reported yesterday. Meanwhile, for me, nothing has changed.
For example, a few days ago I posted a comment that began:
Doesn't it just mean a proposition concerning $x$ and $y$ [$\ldots$]
Like all the other comments I'm talking about, this was rendered normally at the time it was posted. Since yesterday evening, however, it has looked like this:
How insulting! :)
As this example illustrates, even simple uses of MathJax cause problems. That particular comment was a long one, but short comments are also affected. Comments by other users are affected in the same way as my own. (This makes reading the site very difficult!)
I have switched between the HTML-CSS and SVG math renderers, and it makes no difference.
I have not tried clearing my browser cache, partly because this is an often-touted general cure that in my experience has never worked for any problem (whereas every problem has always had a specific solution), and partly because I don't want to risk losing my browsing history, which I refer to several times a day.
I have rebooted Windows and restarted Firefox, without effect. I have also viewed the above comment on another PC, using a different operating system, and an installation of Firefox that has seldom been used to visit MSE, and the problem there is exactly the same.
The problem seems to be specific to Firefox, because the same comment renders normally when I use Opera, even a very old version (2013).
Talking of age: both my computers are very old. One uses Windows XP, the other Windows Vista. I am in the process of replacing both machines, but it is a slow business.
I'm half-resigned to discovering that this problem is yet another good reason for making that long-delayed change. Still, I'm surprised that no-one else has reported the same glitch, so I'm reporting it now.