Go to main menu -> Tools -> Web Developer -> Web Console.
Category Archives: help
How to change Firefox encoding
In Firefox 23, go to the main menu -> View -> Character Encoding, and choose the encoding which you need.
I must say however that the cases, in which I have to use this option nowadays, are extremely rare. This is thanks to the wide use of Unicode, which replaces 8-bit the characters with 16-bit, thus making unnecessary the unreliable language detection.