You can Copy/Paste the content of a synced folder to a folder in the Bookmarks Toolbar folder or the Bookmarks Menu folder. Mobile bookmarks are in a read-only folder (similar to recent type smart folders) and you need to move (copy) them to an actual bookmark folder if you want to make changes.

Thanks for your help, Cor-el. I didn't explain myself clearly. What I want to do is to save a new bookmark to an existing folder. I synced my devices and when I bookmark something new on my computer and I want to save the bookmark to a synced folder, that option doesn't exist. When I click on 'choose', there are no folders that come up. I have to save it to 'other bookmarks' and then drag it to the folder. What I'm wondering is how to save the new bookmark directly into one of the synced folders. Thanks again!