Prism Add-On 1.0b1/Firefox 3.5rc2build2 It is possible to have a Prism app ask for default browser status, and if you say yes, you'll break the default browser check in Firefox. Steps to Reproduce: 1. Launch a Prism App (I have one for Bugzilla, created with the FF Add-On, that shows the problem) 2. Close the window. - At this point, you have the full FF menu bar, not the usual restricted menu. 3. Open Location (not tested with the menu command, use cmd-L) - A normal FF window will open and ask you to make your Prism app the default browser 4. Say 'Yes' (or hit return to dismiss the sheet, my first mistake) Now you're hosed. Your Prism app is the default browser. This is really annoying if you quit the Prism app, as clicking a URL in another app will launch your prism app normally, ignoring (correctly) the URL from the other app. In Firefox, the Default Browser check in Preferences>Advanced>General is now a no-op. Clicking 'check now' does nothing, Checks at launch do nothing, etc. The only way out is to launch Safari and change the default browser pref back to Firefox.