Maybe it helps: it all started after I watched the 2 latest movies of star trek on my iTunes then I tried old movies of star trek and when the sound didn't work I tried them on different software (the sound still didn't work so I guess the problem was in the Files) I Trashed the files but the problem is still here I tried the files on VLC and QuickTime and Divx

When does this happen?

anytime i use firefox

anytime I'm online (when firefox is closed it activates)

You can look at the browser.newtab.url pref on the about:config page and set that pref to the URL of your preferred new tab page. You can use these special pages or set the pref to the URL of your preferred new tab page.

• the default new tab page with the tiles is about:newtab
• the default home page is about:home
• for a blank page you can use about:blank

The browser.newtabpage.enabled pref should be set to true to use the page set via browser.newtab.url as the new tab page.

You can open the about:config page via the location/address bar and search for prefs that refer to this web site (c1.microsoft.com). You can reset user set (bold) prefs via the right-click context menu to the default value.

I read all the websites and too many people have the same problem on firefox and safari (whichever is the default) and it was solved when I removed outlook and I used anti-malware for mac (I don't know which but I don't use outlook anyway)

That looks like the problem discussed here in Apple Support Communities:

• Safari keeps opening the same tab again and again
  https://discussions.apple.com/thread/7094669