I like Opera but I use Firefox as a primary web browser. That's because I miss a feature Firefox has and Opera doesn't.
The feature is Bookmark keywords (shortcuts).
With this feature each bookmark has the possibility to have a keyword and after writing the keyword to the address bar followed by pressing enter on a keyboard, browser will go immediately to the appropriate web site.
Opera has this features only for search engines (called shortcuts).
This missed feature make me to stay with Firefox.