Have temperatures your way makes all temperatures on a page in either Celsius or Fahrenheit. You must edit the script if you want it to display all temperatures in F not C (C is default). There are instructions inside the file, right-click on the greasemonkey icon-->manage user scripts-->pick have temperatures your way on the left-->edit-->read the instructions there. You can also change the number of decimal places.

*Known bug*: All temperatures that are bigger than the rest of the text or are at the start of an element (<x>temp ...</x>) are wrong. I'm putting this up in the hope that someone will see my mistake and tell me how to fix it.