See this article about the New Tab page (about:newtab):

https://support.mozilla.org/kb/new-tab-page-show-hide-and-customize-top-sites If you do not keep changes after a restart then see:

http://kb.mozillazine.org/Preferences_not_saved 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.

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

Could you check whether this preference has been modified:

(1) In a new tab, type or paste about:config in the address bar and press Enter/Return. Click the button promising to be careful.

(2) In the search box above the list, type or paste self and pause while the list is filtered

(3) If the browser.selfsupport.url preference is bolded and indicates "user set" then could you right-click > Copy value and paste it here?

If it is not bolded and indicates default value, then this preference is not the source of the unwanted address. Which leaves the mystery unsolved.

Also, if you double-click and blank out the URL, then restart Firefox, Firefox will stop trying to connect to that address.

Regarding the self-support site, see this article: https://wiki.mozilla.org/Advocacy/heartbeat