To move your Thunderbird 52.6.0 Mail Rules to another Ubuntu PC running the same software (probably works on any computer)
top right as you look at the screen three horizontal lines “display Thunderbird Menu”
“Help”
“troubleshooting Information” click the “open Directory Button” in the Profile Directory line.
“IMAP Mail” (probably “pop Mail if that is what you have).
“imap.gmail.com” (or whatever yours is)
copy “msgFilterRules.dat” onto a flash drive & carry to the other PC and insert
then do the same on the other PC
“Help”
“troubleshooting Information” click the “open Directory Button” in the Profile Directory line.
“IMAP Mail”
drag & drop the msgFilterRules.dat into the “IMAP Mail” folder & when prompted click the overwrite option.
Create folders to receive any redirected mail.
Close Thunderbird & restart.