Make a copy before changing browsers
Open My List and choose Create backup. The displayed text represents supported saved titles and checkpoints from this browser. Keep the complete text somewhere you control. It is not a video download and does not contain an external service's account details.
Merge deliberately
In the destination browser, paste the complete backup into Restore backup and use Merge backup. Existing saved choices are kept rather than treating the import as a command to erase them. Read the reported result and inspect the list afterward, particularly if both browsers already contain checkpoints for the same series.
Know what remains local
There is no automatic cloud synchronization. Clearing browser site data can remove local saved choices. A copied backup remains wherever you stored it, and an older copy will not include titles saved later. Make a fresh one when your list has changed enough that rebuilding it would be inconvenient.