"True story: A few weeks after 9/11 I was in a deli downtown," Johnston tweeted Tuesday. "A bunch of dust-covered firemen walked in (they were still searching the rubble for bodies) & one of them came up to me. He said that he couldn’t believe he ran into me, that all day he & his buddies were trying to Distract each other from the nightmare by talking about their favorite 3rd Rock episodes. He thanked me for helping him laugh during the worst weeks of his life. I started crying, it was definitely one of the most unforgettable moments of my life. I never told anyone before."