Workaround for GM settings migration bug.

src/main/Main.coffee

@@ -84,6 +84,16 @@ Main =
         return
       $.asap docSet, ->
 
+        # XXX https://github.com/greasemonkey/greasemonkey/issues/2600
+        if typeof items.watchedThreads is 'string'
+          changes = {}
+          for key, val of items when typeof val is 'string'
+            try
+              val2 = JSON.parse val
+              changes[key] = val2
+          $.extend items, changes
+          $.set changes
+
         # Don't hide the local storage warning behind a settings panel.
         if $.cantSet
           # pass