If you have previously recommended this thread, you should see a tick / check mark on the recommend button. Click the tick to undo the recommendation (the tick may appear to change to a cross as you do this.) If you added a comment with your recommendation, you will need to delete that from your facebook wall separately.
To go to the desktop site, it asks if you want to do it just now or for always. I always choose 'this time only'. Well, I can't ever get back onto the mobile site. Even if I chose m.mumsnet from the drop down bar at the top