Installing Seamonkey works flawlessly in Hardy. Plugins linked great. Of course I had no prior Seamonkey installed.
In Firefox it appears that reinstalling ubufox helped with plugins if that tells you anything.
Thunderbird is a different story;
I didn't think removing those language packs would be a good idea.
lance@lance-desktop:~$ sudo apt-get install thunderbird
Reading package lists... Done
Building dependency tree
Reading state information... Done
The following packages will be REMOVED:
The following NEW packages will be installed:
0 upgraded, 1 newly installed, 3 to remove and 0 not upgraded.
Need to get 12.0MB of archives.
After this operation, 1032kB disk space will be freed.
Do you want to continue [Y/n]? n