Only the en-US version of Firefox comes with a spellcheck dictionary. Specifically, the en-GB localization doesn't have a dictionary, the user needs to install one.

Some sort of "licensing" issue from what I have read. Mozilla doesn't use files that don't meet its definition of open source. https://en.wikipedia.org/wiki/Comparison_of_free_and_open-source_software_licenses See - Mozilla Public License Need to be a lawyer / solicitor to figure it out.

You can look here for dictionaries:

• https://addons.mozilla.org/firefox/language-tools/

You can see which dictionary is selected if you right-click in a text area and open the Languages submenu. At least one dictionary should be installed and have a check mark to indicate that it is selected.

• Open the "Add Dictionaries" link to install a dictionary if you do not have one.

The spelling checker is enabled if [X] "Check Spelling" in the right-click context menu has a checkmark.

Have tried you suggestion did not work after several attempts,Have now switched back to Firefox 36 and it works perfect. the switch back was done on advice of others who had the same problems with Firefox after 36.

You did confirm via the right-click context menu that check spelling is enabled and that a dictionary is selected?

Start Firefox in Safe Mode to check if one of the extensions (Firefox menu button/Tools > Add-ons > Extensions) or if hardware acceleration is causing the problem.

• Switch to the DEFAULT theme: Firefox menu button/Tools > Add-ons > Appearance
• Do NOT click the Reset button on the Safe Mode start window

• https://support.mozilla.org/kb/Safe+Mode
• https://support.mozilla.org/kb/Troubleshooting+extensions+and+themes