Update available to Firefox 9.0.1 appears every few days, I respond to it but it won't update even tho I wait an hour or two. What can I do?

Every few days I get an update request that says: Update Available. A security & stability update for firefox is available. Firefox 9.0.1 I click install & I have let it run for over an hour & it won't update. I respond to all update requests from all sources with no problem except this one. This is on a MACBOOK PRO. This could be a problem with this computer because I get Firefox updates on my MAC Desktop & there has yet to be a problem. Just to be sure you understand. I get other update requests on my MACBOOK & I have no problems, just Firefox.