Not just on Mumsnet, but everywhere. Moving adverts in the street, even above busy roads: I'm sure that used to be considered "too distracting for motorists". (I know it's not entirely new: I remember the adverts with mechanical triangular prisms which rotated, and being fascinated by them as a child.) Whenever you use any website, there's always something in the corner trying to get your attention, and the bloody "cookies" warnings, which appear a second or two after you open a website.
When did it become acceptable to be bombarded like this all the time, and interrupted every other moment? I remember Youtube before it was full of ads (and videos were limited to ten minutes). I know, these websites have to make money, etc, and it's designed to be so irritating that you sign up for the paid version out of frustration. I miss the days when you could fast forward video through the ads (and I learned that they are designed so that you can still see the product name through the fast forward).
Is one way to deal with it to pick one website such as Youtube, and pay for that, so that you have one place of sanctuary?