Watchlist-openUnread (source) is a script that allows you to open multiple unread watchlist pages with a single button.
To install the script, add:
((subst:lusc|User:Evad37/Watchlist-openUnread.js))
You may also add one or more of the following lines to customise your experience. Replace defaults (the text between = and ; //) with your custom values.
var openUnread_maxnum = "10"; // Preset value for max number of pages
var openUnread_oldest = false; // Preset state of checkbox "oldest first". Set to true for checked, or false for unchecked
var openUnread_showAbove = false; // If set to true the "Open unread pages" button appears above the above the "Watchlist options" box, instead of below it
For compatibility with User:Theopolisme/Scripts/ajaxWatchlist, make sure to set the showAbove option (see § Customisation) – otherwise the button will disappear when the watchlist is updated!
If only a single unread page is being opened when you click the button, this might be caused by your browser's pop up blocker. Try adding an exception for Wikipedia, or adjusting your browser settings or turning off the pop up blocker.