Added a sleep of 50ms before adding the mouseup handler to fix

issue #8.

src/copy-on-select.js

@@ -58,6 +58,10 @@ var CopyOnSelect = {
       this.copy( t.value.substring( t.selectionStart, t.selectionEnd ) );
   },
 
+  sleep( ms ) {
+    return new Promise( ( resolve ) => { setTimeout( resolve, ms ); } );
+  },
+
   async initialize()
   {
     // initialize options from storage ...
@@ -72,6 +76,8 @@ var CopyOnSelect = {
       }
     );
 
+    await this.sleep( 50 );
+
     // add event handler on a target as close as possible to the
     // contents
     let t = document.body || document || window;