At some point I exceeded 500, but I also have firefox simple tab groups (formerly known as panorama) so I'm usually not looking at a window of more than 100 at a time, and any tabs I haven't visited since last launch aren't loaded into ram until I click over to them so they behave more like bookmarks except instead of creating/organizing/cleaning up bookmarks in addition to tabs I just browse/organize/close tabs. Each rabbit hole I go down gets a tab group so if I'm done with a topic I can just close the whole group.