To pin a mission at the moment You Have to open menu click circle icons then drag around to find the faction missions or which ever scenario you are after to then go into that menu then click on the item or mission listed then on to the read the info then back out then pin the mission to make it active.... easy huh

SUGGESTION:

When you open the map it tells you (when zoomed out) that you have something like 3 blue, 2 faction (olive) and a side mission (orange) and maybe the main story line (Yellow) in that province,
Would it not be easier to click on the colour of the mission when you are in map you are after which then lists the say 3 blue items of interest mission while that is listed you can hit space bar on the one your mouse pointer is on and then pin the one you are wanting to choose from.

And: for the games sanity

Make the UI of the mission page zoom-able.

Make 2nd and 3rd custom fit bind-able to a quick key