I was setting up a long-established email account on my new computer, using Thunderbird as I've done for as long as I can remember.
This scary error message came in a popup, white on red:
**Error Creating Account. Ex*Prograrnming bug. Assertion failed, see Log. Stack. *******@resource:***modules *accountcreation*AccountCreationUtilsjsm:***:* *******@resource:***rnodules*accountcreation *AccountCreationUtilsjsm:***:** *******@resource:***modules*accountcreation *AccountCreationUtilsjsm:**:** *******@chrorne:**messenger*content*accountcreation *accountSetupjs:****:** *******@chrome:**messenger *content*accountcreation*accountSetupjs:****:** *******@chrome:**messenger*content*accountcreation *accountSetupjs:****:** *******@aboutaccountsetup:*:****

It happened several times till I finally got it right, putting in the right smtp server. So I thought serves me right, I should have followed Claranet's setup advice.

But of course it is a serious error by Thunderbird programmers and their software needs fixing.

I hope Mozilla read this and take note.