diff --git a/browser_patches/firefox/build.sh b/browser_patches/firefox/build.sh
index 30c630b6cb1dd..b355cd98eebad 100755
--- a/browser_patches/firefox/build.sh
+++ b/browser_patches/firefox/build.sh
@@ -4,6 +4,10 @@ set +x
 
 RUST_VERSION="1.47.0"
 CBINDGEN_VERSION="0.15.0"
+# Certain minimal SDK Version is required by firefox
+MACOS_SDK_VERSION="10.12"
+# XCode version can be determined from https://en.wikipedia.org/wiki/Xcode
+XCODE_VERSION_WITH_REQUIRED_SDK_VERSION="8.3.3"
 
 trap "cd $(pwd -P)" EXIT
 
@@ -19,16 +23,18 @@ fi
 
 
 if [[ "$(uname)" == "Darwin" ]]; then
-  # Firefox currently does not build on 10.15 out of the box - it requires SDK for 10.11.
+  # Firefox currently does not build on 10.15 out of the box - it requires SDK for 10.12.
   # Make sure the SDK is out there.
-  if ! [[ -d $HOME/SDK-archive/MacOSX10.11.sdk ]]; then
-    echo "As of Jun 2020, Firefox does not build on Mac without 10.11 SDK."
-    echo "Check out instructions on getting 10.11 sdk at https://firefox-source-docs.mozilla.org/setup/macos_build.html"
-    echo "and make sure to put SDK to $HOME/SDK-archive/MacOSX10.11.sdk/"
+  if ! [[ -d $HOME/SDK-archive/MacOSX${MACOS_SDK_VERSION}.sdk ]]; then
+    echo "As of Dec 2020, Firefox does not build on Mac without ${MACOS_SDK_VERSION} SDK."
+    echo "Download XCode ${XCODE_VERSION_WITH_REQUIRED_SDK_VERSION} from https://developer.apple.com/download/more/ and"
+    echo "extract SDK to $HOME/SDK-archive/MacOSX${MACOS_SDK_VERSION}.sdk"
+    echo ""
+    echo "More info: https://firefox-source-docs.mozilla.org/setup/macos_build.html"
     exit 1
   else
-    echo "-- configuting .mozconfig with 10.11 SDK path"
-    echo "ac_add_options --with-macos-sdk=$HOME/SDK-archive/MacOSX10.11.sdk/" > .mozconfig
+    echo "-- configuting .mozconfig with ${MACOS_SDK_VERSION} SDK path"
+    echo "ac_add_options --with-macos-sdk=$HOME/SDK-archive/MacOSX${MACOS_SDK_VERSION}.sdk/" > .mozconfig
   fi
   echo "-- building on Mac"
 elif [[ "$(uname)" == "Linux" ]]; then