Rodgers made eight changes to the side that swept aside Slovan Bratislava in the Champions League, but it resulted in a disjointed first-half display.
The back four in particular were very shaky. Pacey forward Alfredo Agyeman got in behind new-look centre-back pairing Stephen Welsh and Auston Trusty with alarming ease, while Barcelona loanee Alex Valle made his debut at left-back and was questionable for both Falkirk goals.
In forward areas, Luis Palma struggled to have any real influence, constantly cutting inside on to his right foot instead of hitting the byeline, and his final ball was lacking.
The Celtic manager's displeasure was demonstrated by a quadruple substitution on the hour mark, with big-money signing Arne Engels introduced alongside Greg Taylor, Kuhn and Yang Hyun-Jun.
It had the desired effect as Celtic began to pin Falkirk in their own half and pop the ball about with confidence.
A rasping shot from Yang stung Nicky Hogarth's palms in the Falkirk goal, and not long after, Idah tapped home Kuhn's cross to level the scores.
Straight from kick-off, Celtic pinched possession high up the pitch and Kuhn fed Idah again. The Republic of Ireland international bullied his way past two would-be tacklers and swept beyond Hogarth to give Celtic the lead for the first time.
Kuhn has shone this season and he took his two goals superbly, dinking calmly over Hogarth after a well-weighted Engels through ball, before lashing in Celtic's fifth from the edge of the box.
Rodgers will be delighted to reach Hampden having gone 2-1 behind, and will be pleased with the way things came together in the closing stages.
However, some underwhelming displays from fringe members of his squad will have raised question marks over their suitability for games against higher-profile opposition.