People who have installed Firefox for Android on HTC Desire by allowing non-market Apps may encounter reboot issues with casual browsing. This article describes a workaround for advanced users.
Install a recent firmware
Android 2.3 and above do not have the issue but, as it has not been made available to users, a workaround is to install another firmware that is Gingerbread like Cyanogenmod 7. For further details about the issue, please see bug 757920.
Warning: You void your warranty when you flash something onto your phone. Before installing a new firmware, you'll need to backup all your data. If you don't follow all the instructions carefully, your phone may get bricked.