Subject says it all: Pop up a confirmation dialog if joining a group would abort or fail your current mission.

This screws up newbies all the time and could potentially result in the loss of some REALLY expensive capship parts if it happened in a higher tier crafting mission.

Might as well extend it to leaving a group too.

The problem with a popup dialog is it can be disruptive while in combat. I vote for a solution that doesn't steal mouse/keyboard control away from your ship.

Right, maybe a warning message in the chat requring you to explicitly abort the mission before joining a group or leaving the group. /mission abort is easy enough to type.

Anyways, the point here is it should warn you if there's going to be mission effects before finding out the hard way.

We could use a modal dialogue in situations where people are already using a GUI to join a group, and require the user to explicitly abort the mission in cases where people use the /group commands.