I can't kill the auto-correcting in Mavericks!
Apple has multiple spelling and dictionary pre-installed.

Many application used them.

You will need to turn of spelling in each application you do not want to use it.

Usually it is simple by right clicking on the misspelled word and disable the spelling in that pop up for Safari, Firefox, Chrome ect. Also every application (word processing) has a menu setting to turn off spelling.

I prefer the way of adding my unique words to custom dictionary.

Example for Firefox



In Chrome is bit different it is called LEARN!