Spell check could be annoying if you are using a lot of abbreviation, short hand writing style, or writing a specific terms which is not recognize by the dictionary. Spell check by default is enable, so whenever you are typing email, Facebook status or new tweets it will check your spelling and underline wrong spelling with a red line. If you are using Firefox here is a simple step to turn it off or on.
1. Click Firefox Button and select option.
2. Click advance and uncheck the box which say "check my spelling as I type".
3. Click OK to apply this setting.
This option will permanently disable spell check until you re-activate it back again by using the same method.
There is another way to do this and it is by changing Firefox configuration. Keep in mind that the first method I mentioned above is the best way to do this. Changing your Firefox configuration (advance setting) can be harmful to the stability, security, and performance of Firefox. Type "About:Config" in the Adress Bar and press Enter, It will prompt you t be careful, click I agree to continue. Look for "Layout.SpellcheckDefault" and double click to open. Set the value to 1 to enable spell check and set to 0 to disable spell check.