With the proximity of the Q and W keys on a QWERTY keyboard, I've suggested several times to the OW developers to have a preference enabling one to indicate if one wants to confirm Quit.
While browsing, I've accidentally pressed Command-Q vs. Command-W more times than I care to remember, thinking I was closing a browser window only to see OW quit entirely, closing a slew of windows I was using in the midst of some research. I've not accidentally pressed Command-Q during a download, but it is really annoying to do it in the midst of research.
If memory serves, Opera had a preference to confirm Quit for this very reason.
I truly wish they would implement this — for me, long-standing — requirement for a "Confirm Quit" preference.