diff --git a/rootfs/etc/cont-init.d/56-firefox-set-prefs-from-env.sh b/rootfs/etc/cont-init.d/56-firefox-set-prefs-from-env.sh
index 3bfa643..8da148a 100755
--- a/rootfs/etc/cont-init.d/56-firefox-set-prefs-from-env.sh
+++ b/rootfs/etc/cont-init.d/56-firefox-set-prefs-from-env.sh
@@ -12,7 +12,7 @@ fi
 mkdir -p "$(dirname "$PREF_FILE")"
 [ -f "$PREF_FILE" ] || touch "$PREF_FILE"
 
-env | grep "^FF_PREF_" | while read ENV
+env | grep "^FF_PREF_" | while read -r ENV
 do
     ENAME="$(echo "$ENV" | cut -d '=' -f1)"
     EVAL="$(echo "$ENV" | cut -d '=' -f2-)"
@@ -36,10 +36,11 @@ do
         sed -i "/user_pref(\"$PNAME\",.*);/d" "$PREF_FILE"
     elif grep -q "user_pref(\"$PNAME\"," "$PREF_FILE"; then
         echo "Setting preference '$PNAME'..."
-        sed -i "s/user_pref(\"$PNAME\",.*);/user_pref(\"$PNAME\", $(echo "$PVAL" | sed 's|/|\\/|g'));/" "$PREF_FILE"
+        sed -i "/user_pref(\"$PNAME\",.*);/d" "$PREF_FILE"
+        echo "user_pref(\"$PNAME\", $(echo "$PVAL" | sed 's|\\|\\\\|g'));" >> "$PREF_FILE"
     else
         echo "Setting new preference '$PNAME'..."
-        echo "user_pref(\"$PNAME\", $PVAL);" >> "$PREF_FILE"
+        echo "user_pref(\"$PNAME\", $(echo "$PVAL" | sed 's|\\|\\\\|g'));" >> "$PREF_FILE"
     fi
 done