I used Opera for years before trying out Firefox 3 when it came out, and adopted it for some small features it had over Opera. Though, when Chrome added the extension support, I made the switch and rarely looked back. The only times I fell back on Firefox was on my older laptop, with Celeron M, 1GB RAM and no dedicated graphics, Chrome was a bit resource heavy to my tastes.
I tried Opera again recently... why can't I appreciate it how I loved it back then?