Keep a complete copy
Open My List and choose Create backup. Copy all of the text from the backup field, including its opening and closing punctuation. Save it somewhere you can return to. The text contains saved catalog identifiers and manual episode checkpoints, not downloaded movies or a streaming-service login.
Merge in the destination browser
Open HDPopcorn in the browser where you want the list, paste the complete text into Restore backup and choose Merge backup. The operation combines supported saved choices. Existing checkpoints in the destination browser take precedence, so a backup from an older device does not silently move an established checkpoint backward.
Read the result
The status message tells you whether the backup was accepted. Malformed text or a backup from another brand is not treated as a valid HDPopcorn list. A catalog entry no longer present cannot become a playable movie simply because its identifier appears in a backup. Check the visible list after merging.
Make a copy before intentionally clearing browser data or moving to a new device. Private browsing may discard local choices when the session ends. There is no account-based synchronization running behind the list, and a manual checkpoint is only the episode reminder you saved yourself.