
With
Opera recently releasing their web browser completely free of Ads, it is a good time to let the truth be told. Not only is Opera Faster then Firefox in all performance areas, it is much more Secure and more Compliant.
Performance
Firefox is often mentioned as a light-weight performance browser. It is also touted as being faster than other browsers. This is far from the truth. These tests clearly show Opera outperforming all other Graphical Browsers in Windows. It should be noted that Mozilla and Internet Explorer both outperform Firefox.
Security
Secunia shows Opera 8.x to only have 1 out of 13 vulnerabilities unpatched. While Firefox 1.x has 3 out of 26 vulnerabilities upatched. Clearly Opera is the more Secure Web Browser.
Compliance
The Acid2 Browser Test is a test page, written to help browser vendors ensure proper support for web standards in their products. Althought the Acid2 Browser Test does not test every web standard, it clearly shows that Opera is more compliant with the features considered most important for the future of the web.
Opera v9 Acid2 Browser Test Results

Firefox v1.5 Acid2 Browser Test Results

Conclusion
With the obvious superiority of Opera to Firefox in Speed, Security and Compliance why is it not being recommended as much? That is a good question. Features that people really care about such as integrated Search, Tabs and Pop-up Blocking have been in Opera way before Firefox even existed. The last obstacle of price is no longer one. Opera is now free.