This changed the behavior in the manner you described with NO change to the website or the ads and is really unavoidable. There MAY be a way to override this, but most sites would never do this, as it would return the long delay before a page will start to be displayed. Too many users will just give up. A study by Yahoo about 5 yeas ago showed a significant decline of completed renderings of its pages if they took over 3 seconds to start displaying. That means real $$$. Sites could reduce ads, but that also costs $$$. Result... You lose.
I run NoScript which nicely resolves the issue as the advertising scripts appear to be rendered instantly, but the typical user would not put up with the issues NpScript causes.