McAfee SA installed on PC, however, curiously....

I have Site Advisor installed on this PC (Vista Home Basic), however, it only works for/on two of the four User Accounts I have set-up. I mean, it is "showing-up" (displayed) in the Firefox "Add-ons" (under Tools) of all of the accounts - but when I do a Search (on Google, etc.), it does not display there, as per normal (with the Green Checks, Yellow Exclamation, or the Red "X" (nor of course the shaded Question Mark), on those two accounts.

Is anyone able to tell me where/how I have blocked this from these two accounts only?

Thanks in advance,
g ...