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Spell Checking in Mozilla Firefox

written by: Percila Jackson•edited by: Michele McDonough•updated: 6/9/2011

The built-in Firefox spell checker allows users to visually check any text they type into a submission form, and displays suggested corrections. It can be tweaked a little by configuration changes, and some experimental add-ons are now available which extend its capabilities further.

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    Firefox's Built-In Tool

    From Version 2.0 onwards, Mozilla Firefox has come with a built-in spell check facility, but this only works for text that the user enters in the page – and then only in multi-line text boxes, as defined by the <TEXTAREA> tag in HTML. Unrecognized words in a text box appear with a red wavy underline, and right-clicking on an underlined word brings up a local menu with the usual options: some alternative spellings at the top, and an option to Add to Dictionary. Further down the same menu, there is an option to turn the spell checking on or off and a Languages submenu which allows the user to choose one or more of the installed dictionaries to use. This submenu also contains an Add Dictionaries option. This links to an add-on page at Mozilla from which new dictionary files can be downloaded.

    Firefox spell checking can also be turned on or off via the Tools / Options (Windows) or Edit /Preferences (Linux) dialog box – look under the 'Advanced / General' tab for a checkbox labelled 'Check my spelling as I type'. Modest users and parents should be aware that the Mozilla English dictionaries contain some (but not all) of the four-letter Anglo-Saxon words generally considered impolite, and will happily suggest them as alternatives, to, say, ‘crpa’ or ‘tist’.

    You can tweak the built-in spelling check to include single-line text boxes as follows:

    1. Enter ‘about:config’ (without the quotes) in the address bar.
    2. Accept the warning about changing settings, and a list of Firefox setting values will appear.
    3. Scroll down to Layout.spellcheckDefault, and double-click on that line to bring up a dialog box with the current value, which is 1 by default.
    4. Change the value to 2 and press OK. Now the checking will be applied to single-line fields as well.

    There are a couple of experimental plugins available from the Firefox add-ons site at, but because they are experimental you will need to register a free account with Mozilla and/or log in to that account before you can download them. Naturally, neither Mozilla nor the developers will take any responsibility for any damage they cause.

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    SpellBound Add-On

    This add-on extends the functionality of text-box spell checking a little further by displaying the contents of the text box in a much larger panel. The user can also specify the size and color in which unrecognized words are displayed. A lot more alternative spelling suggestions are also provided, although the top ones in the list are the same. If you were entering lots of text on a daily basis – for instance, in creating a blog – this might come in very handy. Despite being experimental, it installed and ran with no problems on my laptop under Firefox 3.0. To activate SpellBound, right-click in a text box and select ‘Spell Check with SpellBound’ from the local menu.

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    Spell Checker Add-On

    What if you want to check the spelling of all the text on a web page, not just the bits you type into text boxes? Installing the add-on Spell Checker adds a ‘Spell Check’ item to the bottom of the Edit menu. When this is clicked the current web page is checked to see if it is associated with a language setting. If it’s not, then a warning message comes up: ‘Page language is not specified’, and the plugin quits.

    If the page is associated with a language, however (and most web pages in English appear to be), then a dictionary of words in that language is loaded and all the visible words on the web page are checked against it. This may take a few seconds, depending on the length of the page. Those words that don’t match are flagged with a dotted red boundary, and the user can click on these to see alternative spellings, although they can’t be replaced, of course, unless you have access to the website. Not all unrecognized words generate alternate spelling lists.

    Despite being experimental the add-on worked fine on my system, and the only negative comment I have is that the red outline looked a little ugly, and a more attractive formatting method might be more appealing.

    For full-time website creators, of course, there are spelling checkers built into packages like Adobe Dreamweaver and Microsoft Expression Web. It’s also possible to add a spell checker into a Joomla! installation so that authors can check their articles as they enter them – but those are stories for another day.

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    Mozilla Firefox: Using the Spell Checker []

    SpellBound: Homepage []

    Mozilla Firefox: Spell Checker []