How to run javascript in Firefox mobile on a specific page, on pageload (similar to greasemonkey)

Question

I'd like to run a Javascript snippet at the point where a specific page (e.g. facebook.com) has finished loading to click buttons automatically (e.g. submit form automatically).

So I'm looking for a 'Hello World' Addon for Firefox mobile, that will display 'Hello world' using javascript (alert('Hello World');) when a page has finished loading everything (something using addEventListener('load', ...) probably)

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More Info:

I have tried Fennec guides and dissected a few Fennec addons from the market, but I'm at the absolute beginning when it comes to addon development and am wasting a lot of time on this.

Any (straightforward and easy) resource on this would be really helpful as well, I know there are some Greasemonkeyscript-to-Fennec (e.g. http://geo.inge.org.uk/grease-vervet.php) compilers out there, but they're outdated as far as I can tell.

Answer 1

this is solved by newer versions of Firefox on Android where tampermonkey can simply be installed:

https://addons.mozilla.org/en-US/android/addon/tampermonkey/

for anyone that is getting to this question looking for answers.