So I finally won against the infection.
As you said I downloaded Malwarebytes
. And i did a scan with it.
I also searched in google and found some other forums in which people having the same problem redirected me here http://www.americanp.../portaldosites/
I followed the steps shown ther for manual removal, and I deleted what was left in the add ons and extensions menu.
After that I did another scan with my antivirus program and my computer appears to be clean now.
Good thing there was no need for System Restore ( I haven't done one so far). Thank you guys for the help.