Why does FireFox blank screens when it can't connect?

If I understand the question correctly, it's because Firefox is single-threaded.

A better question might be why Firefox is single-threaded. Apparently it's something to do with JavaScript.

An even better question might be what connecting to a server has to do with JavaScript. I don't have a good answer for that.

A quick search suggests that Firefox 4 will be multithreaded though, so you might be in luck.

Wouldn't it be better to be able to recover the text for storage so you can submit it later?

I've certainly learned to copy my submissions to a text file!