This took a lot of fiddling but ended up taking advantage of TamperMonkeys sandbox capabilities, and added code to get rid of an ad section at the top too.

https://github.com/platima/slashdot-ad-fix/

There's a few other things that can help, that may not actually do anything, but essentially attempt different methods in case of changes or other browser / extension limitations.

Hoping it helps make yours more widely compatible.

Ah, cool. That works for me on TamperMonkey for Firefox with one modification (which I had just needed to make to my own script): instead of confirm returning false, I had to make it throw an exception. Returning false made the page just repeatedly refresh.

BTW, I just put a link to yours in the description here.