Did you really mean 27 or meant 37? Because 27 is more than a year old and not one of the long term support releases, so if you're using 27, you're exposing yourself to all sorts of exploits. If you really meant 27, then I can only guess you're trying to avoid the new theme (which started in 29, so you could have been using 28), and that's a poor reason to stay with an old unsupported browser. Upgrade to 36 and use https://addons.mozilla.org/firefox/addon/classicthemerestore... instead.