Listed under the Enhanced Browser Compatibility section of the version 3.2 entry in the WordPress Codex, I didn’t notice the browser check until updating a different WordPress site from another computer with Firefox 4. After updating to WordPress 3.2, a message appeared on the Dashboard to inform me my browser is out of date.
The service is provided by Browse Happy, a website that links to the latest version of each browser for an easy upgrade.
It looks like I need to update that computer from Firefox 4 to Firefox 5.