The standard method of transferring contacts involves [https://support.office.com/en-us/article/Export-contacts-from-Outlook-10f09abd-643c-4495-bb80-543714eca73f exporting to a csv] and importing to TB. There is another method that is probably easier. First, [https://www.technipages.com/outlook-export-all-contacts-to-vcard-files export the Outlook contacts to a set of vCard files], then [https://support.mozilla.org/en-US/questions/1158501 import the vCards to TB with an add-on]. There is [http://forums.mozillazine.org/viewtopic.php?f=39&t=3010343 a similar 'trick' for calendars].