I believe that the Mac SeaMonkey

I believe that the Mac version of Seamonkey will allow you to specify 
which hard Drive/folder you want it to store the profile in. It has been 
a long time since I launched the profile manager. With the Mozilla suite 
when you launched the profile manager to create a new profile there was 
an option to specify where you wanted the profile stored. I believe that 
if you specified a different location for the SeaMonkey profile than the 
Mozilla profile than each program would use its own profile.

Take care with this tip since I haven't tested it out. My best guess is 
that creating a new profile in a different location will cause each 
program to use its own profile I am not 100% sure. By creating a new 
profile with SeaMonkey you may confuse Mozilla and it might want to use 
the new SeaMonkey profile instead of the old Mozilla profile.  This is 
unlikely. If it does happen it is easy to fix. To fix it go to your home 
folder and navigate to the Library folder and then to the folder titled 
Mozilla. In the folder titled Mozilla you will see a folder called 
Profile. Move the contents of this folder into the folder titled Profile 
that you created with SeaMonkey and things will work again.

In either case my tip is safe to try, BUT for safety Make a duplicate 
copy of the Mozilla folder in the folder Library (this backs up your 
Mozilla profile) just in case something goes wrong and you lose your 
profile. It is better to be safe than sorry.