User:Theopolisme/Scripts/ajaxWatchlist
ajaxWatchlist (source code) is a script that automatically updates your watchlist. After installing it and browsing to Special:Watchlist, new changes to pages on your watchlist will magically appear, no reloading necessary. To install it, add {{subst:js|User:Theopolisme/Scripts/ajaxWatchlist.js}} to your common.js page and clear your cache.
Custom refresh time
[edit]By default, new items are loaded every 20 seconds. To change this, add the following text to the top of your common.js page
window.watchlistUpdateFrequency = ???;
with ??? replaced by the desired refresh frequency (in milliseconds: 20000 = 20 seconds).