[wavefunction]

I could be wrong but it looks like Opera introduced tabs in 2009 with v10.5 while Firefox's first release was in 2002. Unless we're referring to different things.

[xorcist]

That's not right. Opera had tabs in version 4, released in early 2000.

Some people apparently think tabs has to be drag-and-droppable, which Opera had in 2003, in order to be called tabs: https://allthatiswrong.wordpress.com/2011/01/14/opera-did-no...

[meekaaku]

No. Opera from early 2000s atleast had tabbed browsing. It also had gestures, paste-and-go, open non-hyper plaintext links in tab etc.