I haven't gotten this to work, but you can try this:

http://www.iosart.com/blog/2007/06/05/install-google-gears-in-a-xulrunner-app-in-3-quick-steps/

It's written for Prism back before it was called Prism. If you do get it to work, speak up so we can know it works or what other steps it toom you.

Good luck.

ah i should have actually said, i'm running a Mac as well

what i have tried is....

i searched my library folder for prism folders of which there is two, you want the one in application support not caches as that has a folder in it called extensions.

i copied the xpi file into there and ran prism and up comes the familier looking box saying, "
the following items were found in your extensions folder do you want to install them?" etc etc standard firefox box for when you install an extension there

but if you click install it will come up with....

incompatible extension

"Remember The Milk for Gmail" will not be installed because it does not provide secure updates

and then delete the xpi file from the extension folder

I, too, am a Mac user when I have choice over the matter, which is why the article I mentioned was not useful to me, also. Sorry.

I don't know enough about Firefox to offer any further advice; I suspect some googling on that message text would offer some insight. Please keep this board updated if you learn anything further.

i get the feeling it might have something to do with the extension itself so could be up to the monkey to make it compatible, will keep digging but google isn't being my friend today

well i'm now experimenting with stuff i've found here

http://www.luckydisasters.com/2007/10/29/webrunner-now-prism-whatever-heres-how-to-make-an-extension-compatible-with-at-least-one/