Hi, I am having the same problem, with mozilla 1.4 not starting, I had mozilla 1.0.2 which starts just fine, then I "upgraded" to mozilla 1.4 and it did not work.
Posted on 5 forums, but only got answer like "recompile, reinstall, etc.." nothing worked.
Finally, after a week when I tried everything I realized that I could try to move my profile (.mozilla directory) somewhere else and create a new one... et voila' !!
Now, the point seems to be that in spite of the claims, importing a previous profile is still buggy in mozilla.. this is very very annoying.
Hope it will help you too..