After installing Firefox 23, I can no longer find Google as a search engine in my search bar and I also cannot restore default search engines.

search.json => rename to search.json.old
search-metadata.json (if found) => delete
search.sqlite (if found) => delete
search.rdf (if found) => delete

By default, the Google search plugin is installed into this folder: C:\Program Files (x86)\Mozilla Firefox\browser\searchplugins Can you see google.xml there? If not, you may need to reinstall Firefox 23. No uninstallation needed, you can get the installer from the following page: http://www.mozilla.org/firefox/all/ (find your language and OS) ---- If you have google.xml in the usual location, it's possible the data file which stores the search plugins has become corrupted. You can address that by renaming or deleting the files listed below and having Firefox regenerate them. Open your current Firefox settings (AKA Firefox profile) folder using Help > Troubleshooting Information > "Show Folder" button Switch back to Firefox and Exit Pause while Firefox finishes its cleanup, then rename (or delete) the following files: search.json => rename to search.json.old search-metadata.json (if found) => delete search.sqlite (if found) => delete search.rdf (if found) => delete Restart Firefox. Hopefully now Google will be back on the list.