You can copy places.sqlite and favicons.sqlite from your current profile folder to the profile folder on the other device.

• https://support.mozilla.org/en-US/kb/recovering-important-data-from-an-old-profile

You can use the button on the "Help -> Troubleshooting Information" (about:support) page to go to the current Firefox profile folder or use the about:profiles page.

• Help -> Troubleshooting Information -> Profile Folder/Directory:
  Windows: Open Folder; Linux: Open Directory; Mac: Show in Finder
• https://support.mozilla.org/en-US/kb/profiles-where-firefox-stores-user-data

But if I replace the places.sqlite on my new computer with the one from my old computer, It'll replace all the data from the new one with the old one. Is there a way to export my entire firefox history into a file?

If you are on Windows then you can look at this Nirsoft utility.

• https://www.nirsoft.net/utils/browsing_history_view.html

Otherwise you can copy history items to a bookmarks folder in the Library and export the bookmarks.

Using a SQLite utility to export history data (moz_places and moz_historyvisits) might be possible if you are familiar with working with SQLite databases.

SELECT datetime(visit_date/1000000,'unixepoch','localtime') AS visit_date, url, title, visit_count
FROM moz_places, moz_historyvisits
WHERE moz_places.id = moz_historyvisits.place_id
ORDER BY visit_date DESC, url