I'll start by saying that I'm a web usability expert of 10 years.

From a usability point of view, the answer is simply that some people prefer navigating differently, and so the software has catered to the preferences of some users. It's not that all people prefer tabbed browsing, but that it's another option which allows a particular mode of navigation by certain users.

My guess is that firefox (who pioneered this) identified the fact that many users will navigate in a series of stages, being

1 - SEARCH - search for the subject in google (or whatever)
2 - COLLECT PROSPECTS - open each of the links to the pages they are interested in
3 - FILTER TO SHORTLIST - review each of the pages to see which are useful
4 - READ - once filtered, read these pages in more detail.

This type of structured search process is more common amongst very experienced users such as professional researchers, as it allows you to 'switch' from one mode to another, applying different levels of editorial filtering and concentration at each stage.

I cannot provide any references for this, it's simply original thinking based on my experience in the field.

If you were to observe users performing this process without tabbed browsing, you would notice that it is very difficult for them to break off the process at any point, as they have to save each favourite seperately and group them manually. With tabbed browsing, the user is able to save all the current pages at any point, and so they are freed to break off the process and return to it later.

Tabbed browsing also works well for user bahaviours relating to the use of 'live marks' - RSS feeds which allows a group of pages to be opened simultaneously in tabs.

Finally, there is also a technological reason. Now computers are much fmore powerful, users are able to open more and more web pages at the same time, and so better management features for handling large numbers of open windows are increasingly in demand.

There's yet another reason. Have you ever experienced IE's annoying habit of remembering the size of the 2nd, 3rd etc. browser window size the next time you open a 2nd, 3rd window? Tabbed browsing doesn't have that effect. Each new tab opens in a full page (assuming that the web page in question is full screen to begin with). For me, that's a huge advantage.

Personally I like tabbed browsing because it minimises clutter on the desktop. :) Navigating among several tabs within one browser window is more visually pleasing and organised-looking for my desktop as opposed to having many windows open at once.

Here is perhaps an answer more technical in nature you were looking for:

"Browsers that support tabbed browsing enable you to open several web pages in the window at once, all instantly accessible through tabs. This simple functionality provides a powerful increase in web surfing usability, and can quickly become indispensable. The advantages are several:

* No set-up. You don't have to incur the set-up time of the staggered window approach, which must be repeated for each new window you add.

* Scalability. You can conveniently manage a large number of pages at a time with this approach, since a new page is simply another tab. Depending on the width of the window, you can open many as many as a dozen pages or more and still see some title text on each tab.

* One-click action. Mozilla provides the option to open a new tab for a link under the right-click menu. But that is three actions -- right-click on the link, scroll to the option, and then release the mouse. Of course we don't have time for that. Under the Preferences / Navigation / Tabbed Browsing option you can assign the open tab action to several commands, including middle-click. If you have a mouse with three buttons, or a clickable wheel to which you can assign the middle button functionality, then you can activate this option and open new links in new tabs with a single middle-click of your mouse, instantly.

* Breadth-first browsing. With Mozilla you can set an option under Preferences / Navigation / Tabbed Browsing called "Load links in the background", which opens a new page as a background tab without replacing the current page. This means you can continue to read the original page and continue to click on links you want to read later as you come across them without losing the page. In structural terms, this for the first time enables breadth-first browsing, as opposed to depth search browsing where you click on a link, visit and read the page, and then return to the original page to repeat with the next link. Previous to this tabbed browsing feature, the only way to approximate breadth-first browsing was to open each link in a new window -- a feature most browsers provided as a right-click menu item, but was less convenient than tabbed browsing with multiple windows springing up all over the screen."

[source http://www.livinginternet.com/w/wa_browser_mult.htm ]