I finally gave up trying to install the Math extension on my Ubuntu 16.04 system. Instead, I made an extremely simple extension https://www.mediawiki.org/wiki/Extension:MathEasy which only depends on Mathoid, which I intended to be as a temporary replacement for the Math extension, pending the completion of its documentation and/or development.

As a former author of the extension, I have no objection to it being assigned to Robksawyer.

Done.

That problem with the thumbnail error in read-only mode is solved by setting $wgIgnoreImageErrors=true;

That problem with the thumbnails only occurs when in read-only mode, otherwise it works ok. I tried looking at it yesterday, but I didn't see anything. I'm not sure which version caused this problem, my wikis were 1.17 and 1.22 previously. I'll look a bit more at it today, and if I see anything, I'll open a new task.

Thanks for the help in finding a work-around for the problem. Finally, I used memcached to get my wikis to mostly work in read-only mode. The only problem left is a message "Error creating thumbnail: Unable to save thumbnail to destination" which I get for links to .PNG files, but not .SVG files, which I can live with. My settings in LocalSettings.php are:

This should not be LOW priority. It is easy to make the problem happen, and it has a big impact when it does. On my system (Ubuntu 16.04, PHP 7), I haven't found a reliable way to prevent the problem from occurring: