Is there a canonical question where asker doesn't know what a browser extension or userscript is, but is essentially asking how to make one?

I just came accross this: How to import javascript code into developer tools in browser? One time forever

And tried looking for something to mark is as a duplicate of.

I found this: How do I add a simple script to my browser to always run on page load?, which is close, but is specifically asking about Google Chrome.

I found this: Load my custom JS for every page I visit, but it contains a lot of specific context that isn't relevant to the question I want to say is a duplicate.

I tried looking through some of the highest upvoted questions tagged userscript/content-script, but couldn't find one asking something like "what is a userscript?" (Go figure).

Is there a question asking something like "How can I make a client-side JS script only for myself on my machine that can run on any sites of my choosing that I visit using a web browser?" and maybe even asking "What options are there and what are the main tradeoffs?"

Or am I asking the wrong question here? Maybe I should instead be asking (?):

• Should such a question exist at all?
  • Would it be too broad?
  • Should I be voting to close questions in a similar vein to How to import javascript code into developer tools in browser? One time forever for reasons other than being duplicates?
• Should How to import javascript code into developer tools in browser? One time forever be the canonical question that the other ones get considered as being marked as duplicates of?
  • It still contains some user-specific-context (hiding youtube screen cards), but it's much less than there is in Load my custom JS for every page I visit.