What does your feature entail? What is it for? How will it affect existing workflows or user experience?
A previous suggestion was implemented to have mouse buttons four and five map to back and forward respectively, which matches with the behavious of Firefox and Chrome.
Unfortunately, these buttons also simulate a middle mouse button click. This can be irritating, because if you press them while hovering over a link or a large image acting as a link, then you will inadvertently open an additional tab.
This also interferes with some extensions, such as autoscroll.
What are the exact ways that you see a user using your proposed feature? Please go into as much detail as possible, and provide examples of how other browsers/apps implement this feature, if applicable. If your feature suggestion adds on to an existing feature, how would it work into it to extend its usefulness?
This seems to be a feature of Safari and / or WebKit. So it does make sense for the behaviour to be consistent with that. Therefore, I suggest there is an option in preferences to prevent mouse buttons other than button three (the scroll wheel / middle button) from simulating a click and opening additional tabs.
This would make it consistent with Firefox and Chrome, where these buttons only perform forward and back operations and do no otherwise interect with the UI or DOM.