Firefox‘s built-in spell checking feature has been available since Firefox 2. It even has support for multiple languages, which are very useful if your native language is not English.
Simpler Than You Could Imagine
If you have looked around on the Mozilla add-ons site, you might found the page where language packs and dictionaries can be downloaded. At the time of writing this post, 105 dictionaries are available for 86 languages. These packs are actually extensions and you can install them like any other Firefox extension. They will be listed in the “Tools -> Add-ons Manager” menu or by pressing the “Ctrl+Shift+A” hotkey. You can install as many dictionaries as you wish, without limitations.
I use the English (United States) and the Hungarian dictionaries. Both of them suit my expectations. Apart from the dictionaries for certain commercial spell checker components, these open source dictionaries are maintained continuously and new words are added regularly.
Where Can I Find It?
Right click in the text area where you just typed in the text and find the “Check Spelling” item and the Languages dropdown in the context menu.
The Check Spelling command is activated by default. When you click it, the tick will disappear and the spell checking feature will be disabled. The Languages dropdown will also disappear. In the Languages dropdown, you can only see those languages that you have installed. If you need a new dictionary, you have an easy job: Just click “Add Dictionaries…“, and it will bring you to the Mozilla Dictionaries & Language Packs page.
How It Works
The spell checking feature works on any web form. It may be the editor of your blog tool or your content management system, the new topic/reply page in a forum, a comment field, or even a contact form on a web page. Similar to the word processors, an unmatched word is underlined with a red wavy line. When you right click on such a word, you will find suggestions in the pop-up menu, or you can add the word to the dictionary.
Firefox cannot detect automatically the language of your entered text, you have to select it manually in the “Languages” dropdown. Firefox will then perform the spell checking of the text using that dictionary.
Conclusion
Some web based WYSIWYG editors, having their own spell check feature, present a problem, because they may disable Firefox’s right click menu, in addition to this, they may not have a dictionary for your language. In the era of web publishing, the grammatical correctness is not only a human expectation. Due to the sophisticated algorithms of the search engines, it may affect the position of your site in the results list as well.