The Reset Firefox feature can fix many issues by restoring Firefox to its factory default state while saving your essential information. Note: This will cause you to lose any Extensions, Open websites, and some Preferences.

To Reset Firefox do the following:

1. Go to Firefox > Help > Troubleshooting Information.
2. Click the "Reset Firefox" button.
3. Firefox will close and reset. After Firefox is done, it will show a window with the information that is imported. Click Finish.
4. Firefox will open with all factory defaults applied.

Further information can be found in the Refresh Firefox - reset add-ons and settings article.

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Try to reset some preferences to the default with the SearchReset extension:

• https://addons.mozilla.org/firefox/addon/searchreset/

Note that the SearchReset extension only runs once and then uninstalls automatically, so it won't show on the "Firefox > Add-ons" page (about:addons).

Check the browser.search.defaultenginename pref on the about:config page and make sure that it is set to the default value Google.

• browser.search.defaultenginename

• http://kb.mozillazine.org/about:config

Well I had a problem with Bing being the search engine used when entering search query into address bar. Changing default engine name did not help, and maybe that can be changed enough by just selecting other search engine in search bar.

But to the solution. I reseted keyword.URL preference in about:config, and now writing to the address bar uses Google to do the search.