Try forcing Firefox to rebuild the list of installed add-ons to see if it then uses the dictionaries. To do this delete the files as shown in the "corrupt extension files" section of the Unable to install add-ons article.

I tried that now - there are no files which appear to be corrupt ie extensions.ini .cache or.rdf.

Those files will exist, are you sure you are looking in the right place?

1. In the Help menu select "Troubleshooting Information"
2. In the troubleshooting tab click the "Open Containing Folder" button

That will open the profile folder containing those files. If you are in the right place but can not see the full file names, make sure that Windows is displaying file extensions for all file types, for details on how to do that see http://windows.microsoft.com/en-US/windows-vista/Show-or-hide-file-name-extensions

OK I did that and deleted the files. I then unistalled the add-on dictionaries that I had, re-started Firefox and re-installed the dictionaries. The spell check function still does not work. Could it be incompatibility of the dictionary add-ons with Firefox 3.6.10?

The dictionaries should work in Firefox 3.6.10, are they listed in the add-ons manager? (In the Tools menu select Add-ons)

Make sure that automatic spell checking is enabled. In the Tools menu select Options to open the options dialog. Go to the Advanced panel, then select the General tab. Make sure the setting "Check my spelling as I type" is selected.

Do you see those dictionaries on the Tools > Add-ons > Extensions and in the right-click context menu of a text area like "Post a Reply" on this page?

• http://kb.mozillazine.org/Dictionaries
• http://kb.mozillazine.org/Spell_checking

Your above posted system details show outdated plugin(s) with known security and stability risks.

1. Shockwave Flash 10.0 r42
2. Next Generation Java Plug-in 1.6.0_14 for Mozilla browsers

Update the Java plugin to the latest version.

• http://java.sun.com/javase/downloads/index.jsp (Java Platform: Download JRE)

Update the Flash plugin to the latest version.

• http://www.adobe.com/software/flash/about/