On phone: seems great at first, but the toolbar option to disable/enable disappears after restarting Firefox, and you need to go to add-ons and disable and reenable the plugin each time.

Doesn't always work. Varys according to website.

Not able to toggle on/off specific scripts.

The AddOn does what it wants.
It deactivates all JavaScripts on a web page with one click.
Unfortunately, all JavaScripts are enabled by default and not disabled.
It is also not possible to deactivate individual domains. All or nothing.

I can't tell whether it is on or off (or whether it works at all) on Firefox for Android and there seems to nothing that mentions Android at all.