Create a copy before changing browsers
On My List, choose Create backup. Copy the complete text from the backup field and keep it somewhere you control. It represents saved titles and supported series checkpoints, not video files or login credentials. A bookmark alone does not copy these choices to another device.
Merge on the other browser
Open this MultiMovies site there, visit My List and paste the complete text into Restore backup. Choose Merge backup. Existing checkpoints in that browser are retained, while valid new saved references can be added. Read the result message rather than assuming every entry was accepted.
If the import fails
Check that you copied the entire text and did not alter its punctuation. A backup from another brand is not a MultiMovies backup. Unknown catalog entries or invalid episode references cannot create new production records. Keep the original copy until you have confirmed your list on the destination browser.
Browser storage must be available for saving. Private sessions and cleared site data can affect retention. Backup is a deliberate copy you make, not automatic cloud synchronization. Treat it like any personal list of viewing interests and share it only when you intend to.