If you get a message that says an extension can’t be installed in Firefox “”because it does not provide secure updates”, here’s how to work around it:
Start Firefox.
In the Address Bar type “about:config” and press Enter.
Right-click anywhere in the browser window and select New->Boolean.
A box requesting the Preference Name will pop up. Copy and paste the following into the dialog: extensions.checkUpdateSecurity . Press OK.
Select “False” from the next box and press OK again.
From Firefox "Secure Updates" Extension Warning
Filed under: medium
Doesn’t appear this little override hack works in FF 3.6 (OS 10.4.x).