Here is a page from a fork of APEX calculusconverted to PreTeXt:
To experience the issue, scroll to the exercises, and click to open #27. You should see an astroid graph as part of the question.
Then click to open #28 and you should see a squircle.
Now scroll back up to #27. For me with Chrome, the astroid becomes a squircle. With Firefox it does not, but then click on the astroid to make its popup appear, and I see the squircle in the popup, not the astroid.
It's clear that the cause of this is that these images are being made on the WeBWorK server with the same alias, so when the second one is made, it replaces the file on the server. Then anything that would reload the first image on screen ends up showing you the second image. I guess Chrome reloads the image and Firefox does not.
Any ideas on what exactly is causing unique alias production to fail here?