please go to firefox > addons > extensions & remove any suspicious entries (toolbars, things that you have not installed intentionally, don't know what purpose they serve, etc). also go to the windows control panel / programs and remove all toolbars or potentially unwanted software from there and do a full scan of your system with the security software that you have in place and different other tools like the free version of malwarebytes & adwcleaner.

Remove a toolbar that has taken over your Firefox search or home page Troubleshoot Firefox issues caused by malware

Do a malware check with some malware scanning programs on the Windows computer.
You need to scan with all programs because each program detects different malware.

Make sure that you update each program to get the latest version of their databases before doing a scan.

• Malwarebytes' Anti-Malware:
  http://www.malwarebytes.org/mbam.php
• SuperAntispyware:
  http://www.superantispyware.com/
• Microsoft Safety Scanner:
  http://www.microsoft.com/security/scanner/en-us/default.aspx
• Windows Defender: Home Page:
  http://www.microsoft.com/windows/products/winfamily/defender/default.mspx
• Spybot Search & Destroy:
  http://www.safer-networking.org/en/index.html
• Kasperky Free Security Scan:
  http://www.kaspersky.com/security-scan

You can also do a check for a rootkit infection with TDSSKiller.

• http://support.kaspersky.com/viruses/solutions?qid=208280684

See also:

• "Spyware on Windows": http://kb.mozillazine.org/Popups_not_blocked

The Firefox browser does not come with any malware nor is any Mozilla websites infected. Your own computer is what is infected.

This doesn't happen on any other browser nor on any other site. You might want to look into it before telling me it's me.

Is Firefox your default browser because it may be targeting whatever is the default for example.

Again if you downloaded Firefox from a official place like mozilla.org then malware was certainly not bundled with Firefox any version. It would be a very hot topic in postings here and elsewhere if your claims of Firefox 18.0.2 or any release from Mozilla coming with malware was true. Mozilla would lose far too much by doing such as they do not need money.

How about you look into it as for example I downloaded the en-US version for Windows from http://www.mozilla.org/en-US/firefox/all/ and uploaded the file to https://www.virustotal.com/en/

Detection ratio: 0 / 45

https://www.virustotal.com/en/file/a52238f2d3910f0b4a705277c2ee4cd482d924b27d13e945dacafaaaaa331e9d/analysis/

There are some sites out there that do try and bank on the popularity of Firefox by providing downloads with their own toolbars to going as far a not even being Firefox but some spyware.