I can't guess at what you mean by "crashed" or "reboot" here.

If the program crashes and stops, it normally asks if you want to send an error report then starts again.

"Reboot" means switching your computer off and on again, or restarting it via onscreen controls, a reset button, or a key combination such as ctrl+alt+del. I don't get how this relates to a difficulty with Thunderbird.

Try just describing what happens without using technical terms.

If you are actually crashing, see https://support.mozilla.org/en-US/kb/mozilla-crash-reporter#w_viewing-crash-reports and post your crash ID here.