hi, can you please be more specific about what exactly doesn't work (like, do you get any particular error messages), so that we get an impression of the issue?

I put google search engine is the default I click on the default search engine for the address bar, it does not work. but when clicking on the list of other tools such as yahoo, bing ... below, it works! I have changed yahoo, bing ... is the default search engine in the address bar, when I click on it does not work. Yesterday everything was normal.

still not sure what "does not work" really means in your case...

in any case, please go to the firefox menu ≡ > addons > extensions & remove any suspicious entries (toolbars, things that you have not installed intentionally, don't know what purpose they serve, etc). also go to the windows control panel / programs and remove all toolbars or potentially unwanted software from there.

finally, run a full scan of your system with different security tools like the free version of malwarebytes & adwcleaner, which are specialised in adware and browser hijackers.

Remove a toolbar that has taken over your Firefox search or home page

extensions: http://prntscr.com/e22f9m plugins: http://prntscr.com/e22fjg http://prntscr.com/e22fns I've scanned in all! norton security malwarebytes trial adwcleaner iobitbitware fighter pro use DNS google,norton... to block bad sites so i can't fix it. I also use google chrome with firefox. (I also have a little experience with pc.) (perhaps i must reset my pc!)