Also enabling/disabling a script and reloading the page show expected results
Edit: If you are referring to the drop-down issue, it doesn't on my end. If you are referring to whether or not the script works, yes, it does.
Do you have some special options enabled trackingprotection, resistFingerprinting, firstparty.isolate or similar?
Do you have other addons installed and enabled?
Yes. I will disable and see if there are changes. However, unless these are new to FF and enabled by default, nothing would have changed. I do have other add-ons but again, nothing has changed in general. Meaning that I haven't added anything new. However, I am using uBlock Origin so maybe some updated filter list(s) are now blocking functionality. Although I could have sworn I disabled uBlock Origin and had the same result, as well any other privacy add-on that might have been conflicting. This is the first thing I always do to troubleshoot but will double-check and report back.
Edit: disabled everything and the issue still occurs: once the add-on is enabled and the page reloaded, the script disappears from the drop-down menu. The script works, it's just no longer in the drop-down. Again, this isn't every site but I don't enable and disable scripts on a lot of sites. Primarily just Reddit but it may not be the only site this happens on.
One more note: I don't say there is no issue, but without being able to reproduce it, it is hard work on a fix...