You will need some familiarity with the file management of Linux (which I don't have). To create a profile on the other drive, click help>troubleshootinginformation, scroll down to 'profile folders' and click 'about:profiles' and click the 'create profile' button and, from there, define a profile on the other drive. You would then need to copy the profile contents of old folder to the profile on the other drive. Another option on saving space would be to just move the account to the other drive, assuming that it's the account and the messages that take up space. To do that, you could click 'account settings' and on the account page, look at bottom line where it shows the location of the account. You could exit TB and copy the folder to the other drive. Then, restart TB, click the account settings page and click the select button on that line to select the profile where you had copied it to the other drive. Exit and restart TB to verify that all is well. Once satisfied. you could then delete the account folder from the profile.

Unfortunately I couldn't get it to work with any of the options.