I must admit to currently having 280 tabs open. In my case, I open a bunch of things I intend to read (by browsing reddit or the like) and defer the reading of them indefinitely.
In practice, most of the tabs are `legacy' tabs that I don't use, but which I still retain some nominal interest in when I go clean out the tabs every couple months or so. These tabs range from youtube videos that I don't want to forget, to tips for Vim, Wikipedia articles, blog posts on machine learning, instructions for DIY haptic compasses...
About 1/3 can be traced to one or two websites with interesting articles that I intend to read in depth (at some point).