Question

what did thomas jefferson mean when he said the missouri compromise was like a firebell in the night?

did he mean that it was never going to work or something like that?

Answer 1

I am not certain, but a firebell in the night wrecks havoc at the least expected time, and most folks are asleep when it happens. Often , it leads to disaster, as few are ready for it.

Answer 2

At this site scan down to the section on Impact of Political Discourse. It explains what Jefferson thought the Compromise would cause.

http://en.wikipedia.org/wiki/Missouri_Compromise