Chinese： 您好，我是来自中国大陆的志愿者。 你在地址栏输入“about:preferences#search”，然后点击“恢复默认搜索引擎”试试？ English： Hello, I am a volunteer from mainland China. You type "about:preferences#search" in the address bar, then click "Restore default search engine" to try?

This did not work. The option to choose google still doesn't show up.

Your System Details list shows all default search engines as you can see on the "Help -> Troubleshooting Information" (about:support) page, so if you only have Yahoo available then you either have an extension that hides the other search engines or you have malware or there is a problem with the file that stores the search engine configuration

See:

• https://support.mozilla.org/en-US/kb/troubleshoot-firefox-issues-caused-malware

Start Firefox in Safe Mode to check if one of the extensions ("3-bar" menu button or Tools -> Add-ons -> Extensions) or if hardware acceleration is causing the problem.

• switch to the DEFAULT theme: "3-bar" menu button or Tools -> Add-ons -> Themes
• do NOT click the "Refresh Firefox" button on the Safe Mode start window

• https://support.mozilla.org/en-US/kb/troubleshoot-firefox-issues-using-safe-mode
• https://support.mozilla.org/en-US/kb/troubleshoot-extensions-themes-to-fix-problems

You can rename/remove search.json.mozlz4 (and possible search.json, search-metadata.json, search.sqlite) in the Firefox profile folder with Firefox closed to rebuild the search engines registry.

You can use the button on the "Help -> Troubleshooting Information" (about:support) page to go to the current Firefox profile folder or use the about:profiles page.

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

Firefox will rebuild the search.json.mozlz4 file from the builtin search engines.

I wonder whether this could be a side effect of the "Norton Safe Search" extension? Hopefully cor-el's reply will help you determine that. Shame on them if they are hiding all the built-in search engines.

Thanks cor-el. That suggestion of removing search.json.mozlz4 worked for me