Simply mandatory to help make web apps used for the job bearable.

Unfortunately not open source and complex, which may mean that enterprise users may not have permission to use it as enterprise IT departments are tightening their security policies.

And unfortunately, there is another extension of almost identical name ("Tamper monkey" which even uses Tampermonkey's icon/logo), which may trick people into installing the wrong extension. While I have reported this, I think the author of this extension should have more luck to get Mozilla to ban that other "fake" extension.