See [[Make Thunderbird the Default Mail Client]]

Even if you set TB as the default mail client, this kind of MAPI function may still not work. One option that sometimes works is to download and run the full TB installer, set TB as the default mail client during Advanced setup, don't run TB at the end of the setup, then restart the computer. If you currently have 64-bit TB, and the Canon scan software is 32-bit, it definitely won't work. Also, there was [https://support.mozilla.org/en-US/questions/1285243 a recent topic] where an HP scanner wouldn't work with any other mail client besides Outlook, so the trick was to make the device 'think' TB was Outlook.