Open Random Bookmarks от Noodle

This add-on allows you to open random bookmarks from a specified folder. The folder that was selected last will be remembered, so you do not have to re-select it every time. You can specify how many bookmarks should be opened, as well as if every opened bookmark is unique or not. Also has an option to include sub-folders in random bookmark selection.
Once the desired settings are chosen, random bookmarks can be opened either directly in the add-on window, or by right-clicking inside the browser window and selecting "Open Random Bookmarks"