On most websites and forums, it is important to write your messages/text using a "proper" language:
When you post a message on a forum, you should avoid spelling and grammar errors or express yourself in SMS language, as your message may be sudjected to moderation.
Writing a resume or cover letter with spelling or grammar errors, no punctuation, tc, will lower your chances of getting a job!
The corrector Firefox is handy, but has its limitations. It does not correct the agreements between subjects and verbs, does not correct punctuation, endings, do not distinguish between singular and plural.
If you use Microsoft Word, it incorporates an efficient corrector which corrects a lot of errors (as you type)
Open Office also includes a spell checker to flag errors as you type.
Note that: You must first install the dictionaries. However, it does not correct grammar errors.
The free spell checkers have their limitations..
Free and complete on-line correction