I'm running Windows 7 Professional 64-bit, Outlook 2010 32-bit and Thunderbird.
Thunderbird is my default mail client, but occasionally I have to run Outlook. Whenever I do that, the next time I start Thunderbird, it asks me whether it should become the default mail client again.
In Outlook I have unticked the "default program" option.
Any ideas what is causing this? How can I force Outlook to leave my preference unchanged?