You can check if you have the XML files of the default search engines including Google in the browser\searchplugins folder in the Firefox program folder.

If not then you need to reinstall Firefox.

Try to delete the search.json file and possible search-metadata.json and search.sqlite files in the Firefox profile folder to reset the search engines to the default.

You can use this button to go to the currently used Firefox profile folder:

• Help > Troubleshooting Information > Profile Directory: Show Folder (Linux: Open Directory; Mac: Show in Finder)
• http://kb.mozillazine.org/Profile_folder_-_Firefox

Firefox will rebuild the search.json file from the default search engines in the "browser\searchplugins" folder in the Firefox program folder and the searchplugins folder in the Firefox profile folder.

mplv said

the search box (with magnifying glass to the left of it) is completely unresponsive and there are no search options in the options menus/screens. Using the address field in the search bar seems only intermittently to search the web for keywords. a solution would be greatly appreciated.

Thanks cor-el, XML files were missing, so reinstalled as per your advice. Also learned where search data is kept thanks to your second suggestion.

Best

M