HI Ahmed12345 , It seems that your question is unclear , please give us some more info on what you seek to know , anyways i want to tell you that browsers shows this only when the security certificate of the website is expired or not there , you can think of this as a recommended security features but when you want to visit that website you can go in the advance options below in the page where the error comes and opt to i understand the risks and continue option , by doing this you will be able to access that particular website. And have a look at this:- https://support.mozilla.org/en-US/questions/1089558 This is for the windows version but yes it somewhat relates closely. I hope this helps. Have happy browsing with Mozilla. Regards;- gaurav1999