Patrick Dubroy suspects you don’t.
Today he spoke at Mozilla about his very interesting research and field studies regarding how people use tabs in Firefox. He found that people who don’t use tabs really aren’t using the back button much – his participants’ median was once per 50 clicks, and that the more tabs a user opens the less they use the back button.
This really gives voice to some of the thoughts I was having about how the back button and tabs are related. In a sense, the back button is allowing you to go back in history blindly – there’s no way (other than remembering) to know where pressing back will take you. Opening new pages in tabs, however, give you a visual indicator of where you’d been, and allows you to skip backwards in time as far as you need. It can also prevent procrastination by showing you what you were doing (“Right, I was answering an email before I opened 5 Wikipedia pages”).
Another problematic relation between tabs and the back button, as Patrick pointed out, is that your 10 open tabs may all have different back histories. How can you possibly be expected to remember all 10 histories? You can’t, and if you have 10 tabs you probably aren’t using back much as a result.
Another problem of the back button is that it doesn’t work with all media (such as Flash sites) and sucks with web applications (like Google documents). I’ve been trapped many times by accidentally pressing back while banking or using a form, only to find that my data has been lost. These sites tend to offer their own navigation methods.
So, what tabs and the back button have in common is that they are ways to manage browsing histories. Tabs may have made an improvement on the back button, but they still present some navigation limitations.