diff --git a/app/build.sh b/app/build.sh
index 9b024f76a4..8dcdefd9f3 100755
--- a/app/build.sh
+++ b/app/build.sh
@@ -709,12 +709,6 @@ if [ $BUILD_MAC == 1 ]; then
 	xz -d --stdout "$CALLDIR/mac/zotero.xz" > "$CONTENTSDIR/MacOS/zotero"
 	chmod 755 "$CONTENTSDIR/MacOS/zotero"
 
-	# Custom versions of Firefox components (XUL and libmozglue.dylib)
-	# with fixes and workarounds missing in the base ESR build
-	if [ -n "$custom_components_hash_mac" ]; then
-		cp -R "$MAC_RUNTIME_PATH/../MacOS/"* "$CONTENTSDIR/MacOS/"
-	fi
-
 	# Use our own updater, because Mozilla's requires updates signed by Mozilla
 	cd "$CONTENTSDIR/MacOS"
 	check_lfs_file "$CALLDIR/mac/updater.tar.xz"
diff --git a/app/mac/build-and-unify b/app/mac/build-and-unify
index 6974d4846a..19579864fd 100755
--- a/app/mac/build-and-unify
+++ b/app/mac/build-and-unify
@@ -56,15 +56,15 @@ cp x64/$fx_app_name/Contents/MacOS/firefox zotero
 xz zotero
 mv zotero.xz "$APP_ROOT_DIR/mac/zotero.xz"
 
-# Package custom components for fetch_xulrunner.
-# Upload MacOS-<hash>.tar.xz to ${custom_components_url}mac/<hash>.tar.xz and set
-# custom_components_hash_mac in config.sh.
-mkdir MacOS
-cp x64/$fx_app_name/Contents/MacOS/{XUL,libmozglue.dylib} MacOS/
-tar cfJ MacOS.tar.xz MacOS
-components_hash=$(shasum -a 256 MacOS.tar.xz | cut -d ' ' -f 1)
-mv MacOS.tar.xz "$APP_ROOT_DIR/mac/MacOS-$components_hash.tar.xz"
-echo "Custom components hash: $components_hash"
+# Package custom libmozglue.dylib for fetch_xulrunner.
+# Upload the file to ${custom_components_url}mac/ and set custom_components_hash_mac in
+# config.sh.
+xz --stdout x64/$fx_app_name/Contents/MacOS/libmozglue.dylib > libmozglue.dylib.xz
+components_hash=$(shasum -a 256 libmozglue.dylib.xz | cut -d ' ' -f 1)
+mozglue_file="${GECKO_VERSION_MAC//esr}-libmozglue-$components_hash.dylib.xz"
+mv libmozglue.dylib.xz "$APP_ROOT_DIR/mac/$mozglue_file"
+echo "Custom libmozglue.dylib: $APP_ROOT_DIR/mac/$mozglue_file"
+echo "custom_components_hash_mac=\"$components_hash\""
 
 # Save a copy of ChannelPrefs.framework
 #
diff --git a/app/scripts/fetch_xulrunner b/app/scripts/fetch_xulrunner
index 60cd2f90ec..f68f30d425 100755
--- a/app/scripts/fetch_xulrunner
+++ b/app/scripts/fetch_xulrunner
@@ -612,31 +612,50 @@ if [ $BUILD_MAC == 1 ]; then
 		hdiutil detach -quiet /Volumes/Firefox
 	fi
 	
-	# Download custom components (e.g., XUL), as an xz-compressed tarball of the MacOS folder with
-	# custom files in it
+	# Download and extract custom libmozglue.dylib
 	echo
-	rm -rf MacOS
-	if [ -n "$custom_components_hash_mac" ]; then
-		if [ -e "Firefox $GECKO_VERSION MacOS.zip" ]; then
-			echo "Using Firefox $GECKO_VERSION MacOS.zip"
-			unzip "Firefox $GECKO_VERSION MacOS.zip"
+	hash="$custom_components_hash_mac"
+	if [ -n "$hash" ]; then
+		xzfile="Firefox $GECKO_VERSION libmozglue.dylib.xz"
+		# Filename doesn't include "esr"
+		url="${custom_components_url}mac/${GECKO_VERSION//esr}-libmozglue-$hash.dylib.xz"
+
+		if [[ "$(uname)" = "Darwin" ]]; then
+			shasum="shasum -a 256"
 		else
-			echo "Downloading custom Firefox components"
-			echo
-			curl -o MacOS.tar.xz "${custom_components_url}mac/$custom_components_hash_mac.tar.xz"
-			
-			# Verify hash
-			if [[ "`uname`" = "Darwin" ]]; then
-				shasum="shasum -a 256"
-			else
-				shasum=sha256sum
-			fi
-			echo
-			echo "$custom_components_hash_mac  MacOS.tar.xz" | $shasum -c -
-			echo
-			
-			tar xvf MacOS.tar.xz
+			shasum=sha256sum
 		fi
+
+		download_xz() {
+			echo "Downloading custom libmozglue.dylib"
+			echo
+			echo $url
+			curl -fo "$xzfile" "$url"
+		}
+
+		verify_hash() {
+			echo "$hash  $xzfile" | $shasum -c -
+		}
+
+		# Download if file doesn't exist
+		if [ ! -e "$xzfile" ]; then
+			download_xz
+		fi
+
+		echo
+		if ! verify_hash; then
+			echo "SHA hash mismatch. Redownloading libmozglue.dylib…"
+			rm -f "$xzfile"
+			download_xz
+			echo
+			if ! verify_hash; then
+				echo "Hash still doesn't match. Aborting."
+				exit 1
+			fi
+		fi
+		echo
+
+		xz -d --stdout "$xzfile" > Firefox.app/Contents/MacOS/libmozglue.dylib
 		echo
 	fi