Ok, it worked! Basic instructions:
1. Crank up KMail and and create folders with the format option set to mbox as needed to organize your emails. Then copy your emails to these new mbox folders. Once you are done you can close KMail.
2. Open Mozilla Thunderbird and in the Local Folder section create a folder for each of the folders you created in KMail to organize you emails. Now exit Mozilla Thunderbird.
3. then change to the ~./[mozilla]/default/[random char].slt/Mail/Local Folders
Inside you will see 2 files with name that match the folders you created in Mozilla. Ignore the ones with the .msf extention, and create a link to over write the on without an extention that points to the corresponding KMail mbox file.
In KMail you moved all your messages to a single folder called KMailExport that was type mbox.
In Mozilla you created a folder in the Local Folder called OldKMailMesssages

Then the following would create the needed link.
ln -sf /path/to/your/KMailDir/KMailExport OldKMailMesssages

Hope this helps…BTW Mozilla will probably choke to death on a single 1GB mbox file. 😉