Thank you for making me aware of this! Can I ask for more detail ? Can you tell me the advert you were seeing, What device were you using and if seen again are you able to take a screen grab or picture of it ? This way I can fully investigate and hopefully resolve. Thank you RogerMumsnet
Funnily enough it does not happen when I'm using private browsing.
Using a PC. Tried it on Chrome, Firefox and <<the shame>> Internet Explorer. I was logged in when I was using Chrome, but not the others. Currently it's the NSPCC banner, but that changed to a travel one briefly. I think it was this one that crashed by browser as it has a tendency to crash when some multimedia files are run. The screen goes blank and I can't recover the tabs.
The image is of it being a bit stable. At times it flips over to something larger. Normally these banners disappear as you scroll down, but this one does not.