How does that even work? I assumed that Firefox extensions were implemented in frontend web technologies (JavaScript, CSS, etc.)? Do they use WebAssembly or something, or is it just obfuscated to the point that trying to read it isn't worthwhile?
Excerpt from point 4
> 4. NON-ALLOWABLE USES OF TAMPERMONKEY
> You are strictly prohibited from, and agree that you will not, adapt, edit, change, modify, transform, publish, republish, distribute, or redistribute Tampermonkey or any elements, portions, or parts thereof, including without limitation, to any elements, portions, or parts of Tampermonkey software (in any form or media) without the Company’s prior written consent. [...]
this says GPL so unless they update their license file here, this stays
You can of course do whatever GPL allows you to the code in the repository (so up to version 2.9).
If you have a public repository with your code on GitHub, everyone can see the code. But they do not have the right to use the same code in a commercial manner, without you specifying a license for your code, that says they can.