Firefox also has what you describe.
I tried Opera a l-o-n-g time ago, when there was a free version, long before Firefox exited. It didn't use up a lot of memory or disk space, was very fast, and it would let you open up a bunch of browser windows in one main window. Now it has tabbed browsing, like Firefox and Netscape, and tabbed browsing totally rules. Then Opera started charging for their browser, which made me lose interest, and didn't help them gain market share. It looks like they threw in the towel and made the Windows version free again, but they're charging for the cell phone version(s) of their browser.
Each of the browsers have a certain look and feel, but I'm not sure what recommends Opera over Firefox, or vice versa.
We know that IE is a total PoS. How does Apple's Web browser compare? (I think Opera and Firefox come in Macintosh versions).
Edit: Ugghhh....the free version of Opera has a permanent ad banner...you have to pay Opera to get rid of it.
Our lives begin to end the day we become silent about things that matter. -- MLK