5 features Opera Browser did first
slashgeek.net
slashgeek.net
I stopped using the Big O pretty much when Jon Stephenson von Tetzchner did. He went on to found the Vivaldi browser[1]. They gave up on their own rendering engine and are just using Chromium. But Vivaldi is still my browser of choice if only because the gestures and tab ordering work the way I expect them to without having to hunt down plugins.
I remember the F9 quick configuration menu which allowed you to quickly turn on or off certain features, or the custom CSS bar to change the style of a website. Opera was also the first browser with a useful zoom function. One feature which was never adopted widely but was also quite useful were graphical tabs (today this is widespread in Windows and KDE for regular window previews). The list of opera features is kind of endless. It's such a pity this great browser was no further developed.
I wonder why the developers did not open source the code/old engine in a way Netscape did it with Mozilla.
Contrary to what this silly site says, MDI windows are not by any stretch of the imagination _tabs_.