If you right-click on your document, you should see an option to "Open in Browser". Select this option.
If you don't see the option, then you should install the package "View in Browser".
You have to right-click to select this option "View in Browser" after installing.
If you have problems setting up "View in Browser", let me know and I will try and help you with it.
The reason that F12 doesn't work is that either you don't have Sidebar Enhancements installed or you haven't configured it properly.