I now, on average, have ~20 tabs open. When doing lots of fast research or having a very multi-tasking day, it will hit 40 or so tabs. But it doesn't feel like hell, it feels great, because they're all organized in trees/collapsible, and are just a very visible/readable list on the left side.
In normal Firefox or Chrome, I never let myself get more than 15 tabs deep because they're not organized in a meaningful way and feel like unsearchable clutter. With the tree-style tabs on the left, it's really easy to organize/reorganize them and feels more normal to have lots of them open at once if you need.
I unofficially challenge everyone reading this to try that tree-style tab addon for a month and see if you feel more productive/efficient using that over the top-style tabs. It will feel slightly weird at first, but give it that week/month and I bet you'll prefer it when you're done.
Here's the link if you need it: https://addons.mozilla.org/en-US/firefox/addon/5890
Edit: If you're not convinced, tell me which is easier to skim quickly.
This:
* GMail, thorax
* Active by Milest...
* thread sync - Google Sea...
* MSDN - WaitForSingleObj...
* Twitter / Home...
* CNN.com - Breaking N...
* Congressman came under fire in ...
* Jailbird ruffles features ...
* hello - Google Sea...
* hacker news - Google Sea...
or this:> GMail, thorax | Active by Milest... | thread sync - Google Sea... | MSDN - WaitForSinglObj... | Twitter / Home... | CNN.com - Breaking N... | hello - Google Sea... | Congressman came under fire in ... | hacker news - Google Sea... | Jailbird ruffles features ...