Enable spell checking in Firefox Text Fields [Did you know?]

In Firefox, you can enable spell check of a Text Field by right clicking the field and selecting Spell check this field.

However, did you know how to enable spell check by default?
  1. Type about:config in the address bar and hit enter.
  2. Find the preference name layout.spellcheckDefault
  3. Double click on it and change the value to 2.