I'm down to 7800 tabs (30 windows) on my main desktop. 4K on my other, 2K on my laptops. High was >11000 tabs. Firefox makes this easy; takes ~30 seconds to open all those windows and load a tab per window (plus ~8 pinned tabs)

"% string" in the awesome bar completes against tabs only. Helps a ton, along with some about:config settings that open new tabs from pinned tabs at the right (end) of the tab list. Also windows for separate contexts (though tab groups may also work here now, and avoid the overhead of opening a window/loading a tab at startup).

And "About Tabs" extension from glandium (who works for mozilla)