I waned to run two versions of FF on my PC so someone told me to download Firefox "Portable" from "SourceForge / PortableApps.com. So i downloaded it seems like a virus. Wherever i go i get these error messages of "unsafe connection". I get the following message when i go to add on's or a website.  "This Connection is Untrusted

Hello, I waned to run two versions of FF on my PC so someone told me to download Firefox "Portable" from "SourceForge / PortableApps.com. So i downloaded it seems like a virus. Wherever i go i get these error messages of "unsafe connection". I get the following message when i go to add on's or a website. "This Connection is Untrusted You have asked Firefox to connect securely to services.addons.mozilla.org, but we can't confirm that your connection is secure. Normally, when you try to connect securely, sites will present trusted identification to prove that you are going to the right place. However, this site's identity can't be verified. What Should I Do? If you usually connect to this site without problems, this error could mean that someone is trying to impersonate the site, and you shouldn't continue. What is causing this? How do i fix it and is it a virus or junkware?