Use Fira Mono for ... mono

beamerthemem.sty

@@ -43,6 +43,7 @@
 \defaultfontfeatures{Mapping=tex-text}
 \setmainfont{Fira Sans}
 \setsansfont{Fira Sans Light}
+\setmonofont{Fira Mono}
 \newfontfamily\Light{Fira Sans Light}
 \newfontfamily\Book{Fira Sans}
 \newfontfamily\Medium{Fira Sans Medium}

demo.tex

@@ -34,7 +34,7 @@ sanctus est Lorem ipsum dolor sit amet.
   \begin{itemize}
     \item Hello
     \item Hello \emph{you}
-    \item Hello
+    \item htt \url{http://google.com}
   \end{itemize}
 
   \begin{enumerate}