The fact that people do this should not be viewed as a personal failing on their part. This should be seen as an indictment against bookmark UIs. If bookmarks were friendly to use, people would use them instead of tabs.
Ive never gotten anywhere near 500, but if a legitimate number of users are needing 500 tabs open that's a perfectly reasonable use case for a browser that fails to support it.
It's kind of like saying "oh no, people are trying to do x with our platform but it's not built for that..." Well, now enough people are doing this, so it's time to change up your UI / performance.