diff -rup thunderbird-68.0.orig/media/libcubeb/src/cubeb_utils.cpp thunderbird-68.0/media/libcubeb/src/cubeb_utils.cpp
--- thunderbird-68.0.orig/media/libcubeb/src/cubeb_utils.cpp	2019-08-26 23:32:14.000000000 +0200
+++ thunderbird-68.0/media/libcubeb/src/cubeb_utils.cpp	2019-08-30 09:22:26.213301561 +0200
@@ -20,4 +20,6 @@ size_t cubeb_sample_size(cubeb_sample_fo
       // should never happen as all cases are handled above.
       assert(false);
   }
+  // silence the compiler here:
+  return 0;
 }