There's been a lot of unrest as noted in various threads here at HN, more recently [1] where the linked topic offers an insight of preloading a script before it's actually initialised and up and running.

With the average run of the mill site, forums, the problem can be side loading scripts that are doing more than just providing a feature - while many sites eventually time out quickly on a problem script, a few would not ... my solution was to put a lot of POS script sites offering nice (read deep scrape for personal information or refusal of obvious baked BS) features in the deny list, many sites then worked without issue albeit with less features - but a few did not - then they too were added to my deny list.

[1] https://news.ycombinator.com/item?id=48438339