I wanted to ask for clarification. Does activating a mana ability count as an action for purposes of rule 116.4. In other words does tapping a land cause the need for all other palyers to pass priority once again for the spell to resolve.

If you are curious about the purpose of this question it comes up if in multiplayer two players want to counter a spell, but both want to force the other to actualy play out the card.

Activating a mana ability is taking an action, so yes, once a player has used a mana ability, every player will be given an opportunity to gain priority again before the spell or ability on top of the stack resolves.

I'm not curious–I remember this situation being hashed out in Rules Theory and Templating back on the old Wizards Community forums, and know exactly what lies down that particular rabbit hole: misery. I advise not dwelling on it.