Are you talking about duplicated profiles where you have identical mail contacts data and settings, or just two versions of Thunderbird. Duplicated profiles is not available as yet.

With two computers will have to run TB on just this one until I have migrated/copied all other Program/files to the newer computer. Will I then be able to move my profile across? Have already got both Firefoxes syncd. Thanks for your help Chas

yes you can move it. There is I think a support article on the process. There is no "sync" like for Firefox.