Or more reasonably, nearly every major site or service that has ever existed.
It would be better to just have a list of sites that have never had any kind of breach happen. That would be a nice small list for Firefox to track.
The interesting thing is that this is absolutely not true. Just think Facebook or Google.
So maybe this could help change practices to be safer. I think this mindset that "90% of companies don't prioritize security, so we should just accept this" is dangerous. As a consumer, data breaches can cause massive headaches - if you've ever dealt with identity theft, you know this. The security with which companies store their data should be factored into your decision of whether or not to be their customer, because it does affect the value their product provides you.
Perhaps it makes sense to include the date of the latest breach to the shown data breach data.
>it does give users an idea that, at some point or another, the site's security procedures were less than optimal.
We'll see if the big sites like Tumbler end up getting a warning. ;^)