One of my favorite features of Firefox is the automatic spell checking that it does when you are entering text in a textarea. My only compliant is that it doesn't do this for single-line text fields also. Well guess what, turns out that you can configure Firefox to perform spell checking on single-line text fields too. As part of this configuration, you can also turn off the spell checking in Firefox if you desire. Here's how:

-- In the address bar type: about::config.

-- This will bring up a page with a bunch of configuration parameters. Scroll down the list until you find the one called: layout.spellcheckDefault.

-- If you double click on this line, it will bring up an dialog box that allows you to set this value. The valid values are:

0 = Performs no spell checking.
1 = Performs spell checking in text areas
2 = Performs spell checking in textarea and single line inputs