Type about:addons<enter> in the address bar to open your Add-ons Manager. Hot key; (<Control> [Mac=<Command>] <Shift> A)

In the Add-ons Manager, on the left, select Extensions. Remove “ yahoo “ Anything.

Also remove SafeSearch, SearchAssist Incognito, FileConverter Addon, SearchLock, DiscreteSearch, WebSearch, Findwide Search Engine, securedsearch

Now do the same in the computer’s Programs Folder.

Windows: Start > Control Panel > Uninstall Programs. Mac: Open the Applications folder. Linux: Check your user manual.

How to remove yahoo search engine from Mozilla. Till now, i was using google as default search engine but now it is giving result with yahoo, which i don't like. I have tried almost all the option.

"Something" installed a Yahoo search engine for you. Mozilla / Firefox dumped Yahoo years ago. "Options" in Firefox just ain't gonna get rid of it now. You need to find and remove whatever added that to your Firefox installation (as FredMcD mentioned).
Much more common in MacOS versions of Firefox, but much less so with Windows PC's.