I'd like to find out how to use the same profile in a dual boot between Win7 and XP Pro.

Hello docfxit,

try to copy the files from the roaming folder. You can open this folder by typing %appdata% in the "search bar" of Windows 7 or Windows XP. You can find it normally by clicking the Windows "button" in the left corner of your screen.

Do not hesitate to contact us further.

Note that sharing a folder between different OS that use different file paths is not recommended as some files can have an absolute path or other OS specific data.

You can click the Choose Folder button if you want to create or use a folder in a different location.
Make sure to select an empty folder (you need to create this folder in advance) and not a folder that already has files as Firefox will use the specified location in this case.

• http://kb.mozillazine.org/Profile_Manager

You can also create a new profile via the command line.

• https://developer.mozilla.org/Command_Line_Options

You can consider to use Sync to sync the two profiles