Two useful kinds of memory
Save a production with its heart button. On a series page, choose the last season and episode you completed and save a checkpoint. A saved show and a checkpoint serve different purposes, so you can use either or both.
Copy the complete backup
In My List, choose Create backup. Copy all the text in the backup box, including the braces at the beginning and end. Keep it somewhere you can reach before clearing browser storage.
Merge on the other browser
Paste the complete text into Restore backup and choose Merge backup. Recognized titles are added once. Existing checkpoints remain in place, so importing an older backup does not automatically move your current progress backward.
Read the result
The message beside the controls explains what was added or skipped. A backup from another brand is not interchangeable. If the text is rejected, return to the source browser and copy a fresh complete version rather than editing identifiers by hand.