Firefox 3 vs. Opera 9.5? As much as I hate to say this;
Opera WINS. Big time.
This isn't a formal comparison - but let's just consider these things;
* Cold Start Load Time Winner: Opera (by FAR)
* Warm Start Load Time Winner: Opera
* Standards Compliancy Winner: Opera
* Features Winner: Tie!!! Opera lacks features like the cool find and good spellcheck, but firefox is a real resource hog about it.
* Most Likely to be Supported Winner: Firefox (Though YOU can help change that.)
* Cooler Name Winner: Firefox (No contest. Opera is a pretty dumb name, no offense.)
* General Cool Factor Winner: Firefox (Now if Opera goes Open Source and gets a decent ad campaign...)
* Raw Speed Winner: Opera
* Page Load Time Winner: Opera
* Innovation/Integration Winner: Opera (it integrates very well with Linux with full static qt and gtk supported binaries - and it has it's own mail and chat and other cool stuff).