I just uploaded an update to Oil Standard. This version (0.2.1) fixes problems with the crude oil price feed from the mercantile exchange, future proofs the Plug-in & Greasemonkey script against Firefox updates, and enables the Plug-in to auto update itself when future versions of the script are released. If you have a previous version installed, you really should upgrade as your previous version probably doesn't work...
Direct link to the Oil Standard Firefox Plug-in.
Direct link to the Oil Standard Firefox Plug-in.