I think some sort of Malware or Virus appropriated of a root file of my Firefox.

Question

I need help. Every time I reset Firefox and then try to load any website, it gives an 'Untrusted Connection'. This message appears EVEN when I try to open things from the own browser, as the Add-on tab, for example, and it only goes away when I restart the computer. That doesn't make sense. Why does it only happen when I reset the browser?
Also loading tabs is VERY slow, if not stagnant, right now there are four tabs opened, all with very simple websites and Firefox is consuming 390k of RAM.
Right now I clicked on "Automatically add" and it gave me this "The addon could not be downloaded because of a connection failure on support.mozilla.org."
I don't think this is a security software problem, right now I'm using Microsoft Security Essentials, and nothing else. This problem also happened when I used another security software.
Unless there is something else installed on my computer that I don't know.

Answer 1

You can check the connection settings.
*Tools > Options > Advanced > Network : Connection > Settings
*https://support.mozilla.org/kb/Options+window+-+Advanced+panel
If you do not need to use a proxy to connect to internet then try to select "No Proxy" if "Use the system proxy settings" or one of the others do not work properly.
See "Firefox connection settings":
*https://support.mozilla.org/kb/Firefox+cannot+load+websites+but+other+programs+can
Boot the computer in Windows Safe mode with network support (press F8 on the boot screen) as a test to see if that helps.
*http://www.bleepingcomputer.com/tutorials/how-to-start-windows-in-safe-mode/
Do a malware check with several malware scanning programs on the Windows computer.<br>
Please scan with all programs because each program detects different malware.<br>
All these programs have free versions.
Make sure that you update each program to get the latest version of their databases before doing a scan.
*Malwarebytes' Anti-Malware:<br>http://www.malwarebytes.org/mbam.php
*AdwCleaner:<br>http://www.bleepingcomputer.com/download/adwcleaner/<br>http://www.softpedia.com/get/Antivirus/Removal-Tools/AdwCleaner.shtml
*SuperAntispyware:<br>http://www.superantispyware.com/
*Microsoft Safety Scanner:<br>http://www.microsoft.com/security/scanner/en-us/default.aspx
*Windows Defender:<br>http://windows.microsoft.com/en-us/windows/using-defender
*Spybot Search & Destroy:<br>http://www.safer-networking.org/en/index.html
*Kasperky Free Security Scan:<br>http://www.kaspersky.com/security-scan
You can also do a check for a rootkit infection with TDSSKiller.
*Anti-rootkit utility TDSSKiller:<br>http://support.kaspersky.com/5350?el=88446
See also:
*"Spyware on Windows": http://kb.mozillazine.org/Popups_not_blocked