At long last I believe I have the trigger editor working. I have given it some very basic testing, so it is entirely possible that it is riddled with bugs but as far as I can tell, it appears to work correctly so far.
The trigger editor works as follows:
First, select a map. When you do so, you will be presented with a list of triggers associated with that map. In this menu you can press INSERT to create a new trigger or DELETE to delete one. The triggers are currently only named with "Trigger ##" so it may appear as though you're only adding/deleting from the end of the list but this is not the case, as it renumbers the triggers whenever the list is changed.
Once you select a trigger with ENTER, a new menu will appear allowing you to edit various aspects of the selected trigger.
Changing its location will allow you to specify the X/Y coordinates of the tile that will launch the trigger. If you change this, be sure to update the corresponding map tiles accordingly (not possible with my editor currently but I'm pretty sure you can do that with Phoenix's FF4Tools), as only certain kinds of map tiles can launch certain kinds of triggers.
Changing its type will allow you to change whether the trigger is considered a treasure, teleport, or event call.
Changing its parameters will allow you to change the particular details such as which treasure you get or where the teleport will send you. In the case of an event call, you can change which event call is launched, and once you confirm you will be given an opportunity to change the details of that particular event call. The cursor will move to the list of events that are called by the event call and show you what conditions must be fulfilled to execute the currently highlighted event. You can add new events to the event call with INSERT and delete existing ones with DELETE. ENTER allows you to change the currently selected event to a different one. Use the TAB key to alternate between the event menu and the condition menu. In the condition menu, the controls are similar: INSERT to add a condition, DELETE to remove one, ENTER to change the details of the current condition. Conditions are automatically sorted by truth value, so if your condition jumps around after you change/insert it, that is why.
Please let me know if there are any problems. Happy hacking!