userScripts API: re-order without re-registering everything

[tophf]

Currently if we want to register a new userscript to run first we need to re-register all existing userscripts. Many users have a lot of userscripts (50-100), some of the popular ones are larger than 1MB and may have hundreds of match patterns, so that seems wasteful, especially if the user wants to re-order multiple scripts in quick succession testing the result each time.

It'd be nice to be able to set the order explicitly e.g. by specifying before: 'id' in the registration options.

• It's used only during register()/update() to adjust the internal order, i.e. the value is not saved.
• When multiple scripts in register()/update() specify the same before:
  • should they be grouped after that id in the order they were specified in the list?
  • should it be an error i.e. each before must be unique?
• A non-existent id should probably result in an error.

[kiaraarose]

Safari doesn't support the UserScripts API but we agree that it would be nice for developers to have a way to set some priority for these user scripts.

[Rob--W]

Note: Chromium has an issue tracking the order of user script execution at https://issues.chromium.org/issues/337078958