specify static main world script in manifest.json

[marcustyphoon]

Description

Yep: this works.

Rather than creating and appending a script element to run the main world script in the correct world, this specifies it as a static content script with the "world": "MAIN" property.

My assumption is that content scripts get injected in order and are executed synchronously...? So there, uh, should be no race conditions with this? Probably?

Requires Firefox 128, which was released today, so we obviously don't want to do this now.

Testing steps

[marcustyphoon]

• make main_world script classic, preventing Uncaught SyntaxError: redeclaration of const moduleCache (will be done with Fix extension restarts in Firefox #1551 merge)