/ sed replace w/ variable

https://askubuntu.com/questions/76808/how-do-i-use-variables-in-a-sed-command

scripts/99_deploy.sh

@@ -320,7 +320,7 @@ if [ ${operation} == "dots" ] ; then
         file_name=user.js
         file_path=${ffpd}
         deploy_file "${dots_trg}/firefox/${file_name}" "${file_path}/${file_name}"
-        sed -i -e 's/{HOSTNAME}/${HOSTNAME}/g' "${file_path}/${file_name}"
+        sed -i -e "s/{HOSTNAME}/${HOSTNAME}/g" "${file_path}/${file_name}"
 
         file_name=userChrome.css
         file_path=${ffpd}/chrome