I just helped a person move from mac to PC with no problems, so the same should be true in reverse. My personal preference is to first install thunderbird, exit, and then use the OS's file management tool to copy the profile to overlay the default profile. That guarantees it is identical to what was on PC. Or, you could use tools>import>import from another thunderbird installation. IMPORTANT: be sure the profile on PC was created when Thunderbird was NOT running. Another option would be to copy profile to somewhere on hard drive, click help>troubleshootinginformation, scroll down to 'profiles' and click 'about:profiles, click the 'create profile' button and follow the prompts to name it and click the browse button to locate and select the profile you copied.