I spent an HOUR writing a post...fearing the worst (ie logging in at the bottom without copying said post because sods law, it always gets lost), trying to highlight said post to copy, I happened to click on the new mumsnet bar at the top and lose the whole thing! Menacing gggrrrrrrrrrr..
Why oh why does that bar keep popping up, I hate it (whimper)
YANBU at all. Sorry about this. You can hide the side bar by going into customise , scrolling down to 'other options' and changing 'Hide the viewport bar (A.K.A. slide bar)' to 'yes'. Don't forget to click save and the bar should disappear.