The recent problem with the https link in the mathjax filter (MDL-46748: briefly, an https web address needed by mathjax became outdated) seems to have revealed a moodle design flaw. In this case, the minor problem should have resulted merely in tex in websites not being properly rendered. In fact, it disabled site editing (among other things, the file picker stopped working). I don't know the code details, but file picker operation should not depend on the correct performance of the mathjax (or any other) filter. I can only guess that the file picker makes a call to possible filters, but does not time them out. This seems a fundamental flaw: surely calls to filters (and probably other classes of plugins) should be wrapped in timeouts.