I've presently got 2 tabs open: HN and this comment form.
Even when neck deep into documentation or github issues I don't think I've ever gone above 20 tabs, it definitely doesn't seem like it could be productive.
Things like: Gmail, calendar, Xero, time tracker, things I've been meaning to read but haven't yet put in a TO READ folder (sometimes hits 30+ tabs), Trello, business plan lists, BitBucket for an iOS project, Shopify partner admin, Font Awesome cheatsheet, 15-20 client projects I might work on in any given week including their admin backends, App Annie, Analytics, trip research (20-40 tabs easily on maps, spreadsheets, itinerary suggestions, Airbnb, Booking.com, hotels, national park sites), 5 tabs currently devoted to trying to work out how to get a National Geographic subscription to work on device and web, and so it goes on.
So then you devote a couple of hours to going through and closing tabs, and find you still have 300...
The solution, if anyone ever gets this far down the page, is to use Session Manager to save the tabs, close Firefox, and then just uncheck the boxes for the tabs you don't ever want to reload.
I just can't stand if my browser has so many tabs open I can't read the what the hell it is from the header and since I always use browser only on half of my screen with editor on the other side (actually since I have 21:9 screen I've split it in 3 so I can have project | editor | docs) that gives me at most like 15+-5 tabs to work with.
But maybe I'm just the weirdo out of everyone.