There is a conflict between automatic and manual checking for updates. Steps to reproduce: 1. Adjust settings so that Firefox checks for updates automatically and then asks what to do. 2. Install an old resease of Firefox (or wait for a new one to become available). 3. Wait for the small box about available update to appear, but don't click on it. 4. Wait some more and then click Help > About Firefox > Check for Updates 5. If the timing was right, the automatic update checker will pop up the window asking what to do about the update while the manually started download is in progress.