For me, there continues to be a single deal-breaker: single-window mode is not standard, and, on OS X, cannot be activated by extensions. Single-window mode is when links from external applications, or any calls for new windows inititated by scripts on web pages, load in new tabs rather than in new windows. As a user who tends to have upwards of 50 windows open at a time as he does research on various databases, it's important to have this feature. The same problem exists in Mozilla.