When burning .thunderbird folder to a cd/dvd it changes the r/w priviledges in Mail folders to r only. and you say no way, well i'm sitting here looking at the mail folders on the dvd and all of them say 'read'
In the past I noticed if I move the .thunderbird folder onto a hard drive or flash drive I had no problems of putting the .thunderbird folder onto a new upgrade/install and it would work perfectly.