Can't be certain of the cause, but upon installation into SeaMonkey 1.1.16, the dialog box mentioned 1.9.2.4.

Restarting & About NoScript shows 1.9.2.5.
A second (or is it a third) install now, & the install dialog box has hung?

Cancel was ineffective, the dialog remained.
Quitting the browser did actually quit.
That hang may have been an oddity. Installing yet again, completed successfully.