I don't use Ubuntu. I use raw Debian.
And I heard report of this problem from other distros as well, e.g.
As for SeaMonkey package, I used
the seamonkey-1.1.18.en-US.linux-i686.tar.gz package from Mozilla's
server since Debian dropped IceApe (aka SeaMonkey) a few months ago. :(
And with the package from Mozilla servers, the NSS installed in your
system shouldn't matter at all, as our packages use their internal NSS.
As we're using the same NSS in 1.1.18 as in 2.0b2, and apparently 2.0b2
doesn't have that problem on the same machines, it looks very much like
the problem isn't even NSS itself, but how we actually load it.
If I just would understand any of that code...
support-seamonkey mailing list