Your malware infected that means. Unless you can boot your system into Safe Mode with Networking your not going to get rid of it. This requires either you find a solutions on the net or take to a computer shop to clear out the infections. That is something not of Mozilla forum doing.

See if any of these links can help; https://www.bing.com/search?q=https%3A%2F%2F123.sogou.com&pc=MOZI&form=MOZSBR

temfrong said

mozilla frequently shows https://123.sogou.com in home page, altough i have set it in setting section , is there virusses in my laptop?

If this is with the Linux system you are posting with then it is not likely due to any viruses as that is more of a Windows issue as above two posters are on about.

https://support.mozilla.org/en-US/kb/how-to-set-the-home-page