First Officer reported lack of compliance with MEL procedures allowed the aircraft to operate in revenue service with non-operational fire protection. After departure; it was noticed by the Captain that three circuit breakers were found to be out. The flight crew continued to the destination airport and turned the aircraft over to maintenance for action.

Narrative

I am new to the fleet. Coming from the overnight in ZZZ; we were both selected for Known Crew Member (KCM) random screening. We arrived at the airplane and I felt busy; but not rushed. We had an MEL related to a fire loop/fire protection. I did the walk around and when I came back to the cockpit; it appeared as though we were done boarding already. When I reached the fire/overheat test of my pre-flight flow; something did not look right. I only saw one side passing the fire test. I then got confused; but remembered the MEL. I re-tested each; and grabbed the Captain's attention. I asked does this look right with our MEL? As I pressed each fire test. He responded that yes it was correct. Upon reaching cruise; the Captain noticed that 3 circuit breakers were popped on the overhead. They were the fire protection l engine 1 and 2 and the fire detection alternate power l. None were collared. We both became confused as to the write up. We looked at the MEL; it was the right side that was written up. I honestly do not remember exactly what I saw during the pre-flight fire/overheat test; I think I only saw the right fire message; not the left. I assumed that the left side was the MEL; as I only saw the right associated message. Upon further de-brief; the Captain was doing his T/O configuration check at the exact moment that I grabbed his attention and I did the second set of fire protection tests. He assumed I was asking about his T/O configuration test; not my fire protection test. There were extra messages at the time; I knew they were related to his test; and I think that added to my confusion. Bottom line - I think that we flew a leg without any functioning fire detection on the left motor. We made a maintenance write up about the circuit breakers.A contributing factor is the way in which our maintenance write ups are written. It is almost as if they are made to be confusing on purpose; leaving us to hunt for Easter Eggs with every MEL. Both the left and right engine fire loops are mentioned. Yes; I get it. As long as you have one functioning loop on each engine then you are good. Still; I see both the left and right mentioned. Simplify the language for each MEL; and the maintenance release altogether. It is just like the NOTAMs can be sometimes. It is as if we are set up to fail; we have to hunt for Easter Eggs every day; every leg; day in; day out. It is a never ending barrage of possible gotchas. This release alone had 26 pages of maintenance information. 26.