The files that hold the search information may be damaged.

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.

Type about:support in the address bar and press enter.

Under the page logo on the left side you will see Application Basics. Under this find Profile Folder. To it’s right press the button Show Folder. This will open your file browser to the current Firefox profile. Now Close Firefox.

Locate the above files. Then rename or delete them. Restart Firefox.

Is the problem with:

• a Firefox search bar/box, such as the search bar, address bar, built-in home page or new tab), or
• the search box on a Google site, such as https://www.google.com/ or one of the country-specific sites?

A user reported a problem on https://www.google.com.au/ where the results would not show below the search box when entering the query on the page. The workarounds were:

• use Firefox's search bar, or
• turn off Instant prediction search

See: Google search = blank screen (no results at all)

Hopefully a real solution will be found.