Is there any web site where you can upload JSON Firefox bookmarks file and then manage the bookmarks?
There is a plug in called xmarks that does via an account that you sign up for when you install it. It also stores them so you do not lose your bookmarks when you switch from browser to browser.
I don't know of any that supports JSON files.
If Firefox HTML bookmark files are an option, too - then SemanticScuttle is the tool for you.