hackademix.net

This morning I got many reports about NoScript disappearing after a Microsoft automatic update.
Looks like a "fix" for the infamous .NET Framework Assistant (AKA the ClickOnce extension for Firefox) caused the breakage.
Luckily this issue is temporary: just reboot your system and everything should be fine (in the best MS tradition).

Update:

Looks like the .NET Framework Assistant keeps causing troubles to many extensions (including NoScript) even after a reboot.
My ultimate advice is uninstalling it and, if needed, fixing the Add-ons Manager corruption which may be happened.