AIBU to be cross because.....

[TheFrogs]

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)

It has a life of its own

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.

hth

Best
MNHQ