Comment 7 for bug 261595

Yes, the space isn't reserverd. But I don't think we've two copies on disk while
rewrite. We open popstate.dat with PR_TRUNCATE and write it from scratch.
Overwriting a 1.5 kB popstate.dat with a 1.5 kB popstate.dat should succeed in
any case (except the very rare and unlikely rapidly filling).

Dave, how was the situation you had? Wasn't there any byte free after Mozilla
gave up?
And did Mozilla even start downloading and then stopped after a few mails? Or
did it recognzie there isn't enough space before downloading the first one?