Personal data and customizations are stored in the Profile folder. https://support.mozilla.org/en-US/kb/profiles-where-firefox-stores-user-data It is fairly easy to transfer those files to a new Profile on the new device. https://support.mozilla.org/en-US/kb/back-and-restore-information-firefox-profiles

These add-ons can be a great help by backing up and restoring Firefox '''[https://addons.mozilla.org/en-US/firefox/addon/febe/ FEBE (Firefox Environment Backup Extension)]''' {web link} FEBE allows you to quickly and easily backup your Firefox extensions, history, passwords, and more. In fact, it goes beyond just backing up -- It will actually rebuild your saved files individually into installable .xpi files. It will also make backup of files that you choose. '''[https://addons.mozilla.org/en-US/firefox/addon/opie/ OPIE]''' {web link} Import/Export extension preferences