I am really sorry for this sir . But we are not giving any wrong information to others. If we said that our site haven't any malware then we are sure about that. But though its happening & also you are a experienced then here must have some problem . For this we need your pardon sir . Please be with us & as like that we will must solve our problem .

Specifically, what leads you to believe that you got Malware from a Firefox download?

You ended up installing something called "Fat Browser"??

To track this down, it would be helpful to know:

• Does your history show the ultimate download URL from which you got the Firefox installer? There is a redirect between the main Firefox site and the server that hosts the files. It would be useful to know if that got hijacked somehow.

• If you still have the installer you downloaded:
  1. Was it the full/offline installer or the "stub" installer that connects back to download one or more additional files? Usually you can tell from the file name or size.
  2. Could you upload the installer to VirusTotal for scanning and post a link to the page showing the internal metadata of the EXE and the site's detections? https://www.virustotal.com/

• Can you provide information on any malware detection by your security software?

• If you did not remove your Firefox profile folder after uninstalling, could you upload the contents of extensions.json to a site like Pastebin (pasting Javascript here will create a mess). That file should be here:

C:\Users\username\AppData\Roaming\Mozilla\Firefox\Profiles\semi-random-profile-name\extensions.json

Also if your claim was true it would be a very hot topic here, at independent mozillaZine forums and tech sites around.