Back then, the O is obviously looked like it was handwritten.
This is the logo of Opera since 1999 until 2001. Back then, the O is smaller than its own shadow. Also, the font of the O changed.
This is a remade version of the former logo. The O is now bigger than the old one and its texture is now flat.
The O is now thicker and 3D. However, this also happened to the shadow.
The perspective shadow was replaced by the shadow underneath it. The O's texture was changed to plastic.
The logo is thinner. The shadow, however, became even smaller. and almost disappeared.
The shadow disappeared literally. The O's flat 3D texture was changed to a ring. The font also changed again.
See also the logos of its main software where the logos are from: Opera Software