Get rid of that yahoo search in firefox

I was unable to change the search engine in my Firefox. I had changed it several times but the next time with all the surprises I would see it reverted back to the default Yahoo search, that is actually not useful to me. I found it very annoying though. Anyway I did some googling to find a way out, but not that useful! so here is a solution finally got me out of it.

1- open firefox and enter "about:config" in the address bar. here you can see the configuration parameters.

2- search the word "yahoo"in the search box in upper part search bar.

3- change the value of the parameter "browser.search.defaultenginename" to "Google".

4- change the value of the parameter "searchreset.backup.browser.search.defaultenginename" to "Google".

5- change the value of the parameter "searchreset.backup.keyword.URL" to "http://www.google.com/search?lr=&ie=UTF-8&oe=UTF-8&q=&#8221".

6- done!

Yahoo search is not that bad but I personally prefer Google, beside when you want to do some search in Persian, it just sucks man! but in return Google handle it very good. so why should I use Yahoo!