Create your copy
Open My List in the browser holding your saved titles. Press Create backup, then copy all the text in the backup box. Keep it in a note or file that you control. Creating the text does not delete the existing list.
Merge on the other device
Open Series9 on the new browser, visit My List and paste the complete text into Restore backup. Press Merge backup. The result tells you how many titles or checkpoints were added and whether any entries were skipped.
What stays unchanged
The merge does not replace a checkpoint already saved on the receiving browser. This avoids moving a series backwards if you have watched more episodes there. Duplicate saved titles are not added twice. An unavailable catalog entry is skipped rather than replaced with a different movie.
If the text is rejected
Check that the beginning and end were included when copying. Other brands' backups and arbitrary text are not accepted. Your backup should be shorter than the input limit shown by the page. Recreate it from the original browser when possible instead of editing title identifiers by hand.
No account required
This is a manual transfer, not automatic cloud synchronization. A person with the backup text can read your selected title identifiers and episode notes, so share it only where you intend. The privacy page describes what is stored locally.