I switch browsers every year or so. Last year Chrome was my default browser after switching from Firefox (which had become achingly slow), and I switched from Chrome to Safari because it supported 1Password. While Chrome now supports 1Password integration, I am happy with Safari and don't see a reason to change.
The only thing I miss from Firefox is the Merge All Windows function. You could hit “⌘-SHIFT-M” and all your windows would be gathered in one window with tabs. (Though, now I can't find this feature and I'm wondering if it was a plugin I'd used.)
Safari has this feature, but not accessible with Keyboard Shortcuts. Here is the menu as it looks before you do this. The option is there, but you have to grab your mouse and select from the menu.
By the way, this also doubles as a tutorial for adding command keys to any application's menu (as far as I know) in OS X.
Open up System Preferences and choose "Keyboard" and then hit the "Keyboard Shortcuts" tab.
Select the little plus sign in the center of the window and in the popup select Safari for the application and type "Merge All Windows" (the wording is important) for the Menu Title.
For the Keyboard Shortcut box, simply type the shortcut “⌘-SHIFT-M” and it will fill it in for you.
Click "Add" and now head back to Safari. Your new Keyboard Shortcut is now in place.