Possibly related: Google comes up blank.
My userscript here seems to cause issues when I use it in Firefox.
Google searches come up blank, though I can inspect and see the code.
However, the main thrust of this issue (since I can band-aid the previous one by excluding certain sites) is that the editor tools on StackExchange sites disappear, as does the tags dropdown. Here is a screenshot of what I'm describing.
It's probably going to be a straightforward fix that I've missed because I don't have a scripting background, but I'm not sure where to look to fix this.