It's possible to import your history from Firefox into the History Trends Unlimited Chrome extension. Follow the steps below:

1. Before you begin, you should back up your history in History Trends Unlimited, so you can restore it if something goes awry.
2. Find out where your Firefox Profile directory is located: In Firefox, visit about:profiles, find the section for your profile, and make a note of the "Root Directory".
3. Install "DB Browser for SQLite" for your operating system from here: http://sqlitebrowser.org/
4. Close Firefox.
5. Open the DB Browser, click "Open Database". Navigate to the "Root Directory" for your Profile and open the "places.sqlite" file.
6. Click the "Execute SQL" tab.
7. Copy and paste the following SQL into the SQL box:
   • SELECT moz_places.url, 'U' || (moz_historyvisits.visit_date/1000), CASE moz_historyvisits.visit_type WHEN 1 THEN 'link' WHEN 2 THEN 'typed' WHEN 3 THEN 'auto_bookmark' ELSE 'unknown' END, moz_places.title FROM moz_places, moz_historyvisits WHERE moz_places.id = moz_historyvisits.place_id ORDER BY moz_places.url
8. Click the play icon (Execute SQL). The results should appear below.
9. Click the button underneath the results and select "Export to CSV".
10. Uncheck the "Column names in the first line" checkbox.
11. Select Tab as the Field Separator.
12. Select the blank option for Quote character.
13. Select Windows for New line characters.
14. Click Ok.
15. Select a location to the save the file and click Save.
16. Finally, import the file into History Trends Unlimited via the "Import History" section in the Options page.