This Old Code

Are user web site provided spell checkers obsolete?  With the advent of Google tool bar and the built in spell check for FireFox do we need to provide our own custom spell check for our website controls?  The only case where I can think of this still being relevant is when dealing with a very special set of vocabulary such as finance.  But even in this case if the user customizes the FireFox spell check to their diction across the board my site spell check is mostly irrelevant and frankly less useable then the web Browser spell check