There are three channels from which you can install Scriptish, the official Mozilla Add-ons channel which is the most stable and least current, the staging channel which is usually stable and updated a little more frequently, or the nightly channel which is updated every day and far more likely to have problems.
Mozilla Add-ons site
The Mozilla Add-ons (AMO) release is reviewed by Mozilla’s AMO Editors who diligently test and review the source versions released through this channel. So it is by far the most stable, and least current version.Install! From addons.mozilla.org
Every night a new installable add-on file is produced from what is currently in the developer repository, for brave users to test.
Beware: Nightly builds might be unstable or outright broken!
Download nightly builds