Access multiple SessionSync folder

[gasparakos]

I use Floccus (https://floccus.org/) to sync bookmarks from multiple nextcloud server. It was mentioned in #68 (comment) that the addon just selects the first SessionSync folder. It would be great to concatenate/access all SessionSync folders from different syncs/sources. Maybe easier to implement an option to choose which folder to use. What about a drop down next to Sessions, History in the top left corner of Session Sync window for different folders?