I suspect one of your extensions may be generating the tab. Could you try disabling ALL nonessential or unrecognized extensions on the Add-ons page. Everything you can live without for 48 hours. Either:

• Ctrl+Shift+a
• "3-bar" menu button (or Tools menu) > Add-ons

In the left column, click Extensions. Then, on the right side, if in doubt, disable. (Note: Adblock Plus, Adblock Plus Pop-up Addon, FireFTP and Tab Mix Plus should be fine. Probably also Video DownloadHelper.)

Often a link will appear above at least one disabled extension to restart Firefox. You can complete your work on the tab and click one of the links as the last step.

If you keep an eye on it for the next 24-48 hours, do you notice any change?

You can check the target line in the Firefox desktop shortcut (right-click: Properties) to make sure that nothing is appended after the path to the Firefox program.

The target line is fine and nothing is appended.

I disabled the one click video downloader and seems like it is fine for two days already.

Thank you, I will mark this as solved if it doesn't pop up in two days.

Sorry, popped up again today.

Does the Bing page open with a particular set of search results, or just the home page? Are there any parameters in the address bar that might help track down the culprit (sometimes affiliate codes or other indications are included)?

It opens with just the homepage. I didn't turn on my router early enough today, so I did get a glimpse that it was loading a microsoft page before switching to bing, but it went too fast and I cannot see the whole address. Back does not work and history shows nothing of that sort. Sorry for not being able to provide more info.

A redirect that occurs only at startup is difficult to catch using the Developer Tools.

If it happens at other times, you could try opening Firefox's Browser Console (Ctrl+Shift+j) and keeping that window minimized. It should continuously log all the URLs requested.

I assume you have Firefox on its default setting of diverting new windows to new tabs instead. To try to detect an externally generated launch, could you switch a setting which governs whether externally generated requests open in a new window or new tab so those can be distinguished from internally generated requests? Here's how:

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

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

(3) Double-click the browser.link.open_newwindow.override.external and edit it to 2 and OK the change

For future reference the options are:

-1 = apply the setting in Options>Tabs to external links (default) 3 = open external links in a new tab in the last active window 2 = open external links in a new window 1 = open external links in the last active tab replacing the current page

You can check for recently installed suspicious or unknown extensions.

• https://support.mozilla.org/kb/Troubleshooting+extensions+and+themes

Do a malware check with several malware scanning programs on the Windows computer. Please scan with all programs because each program detects different malware. 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:
  http://www.malwarebytes.org/mbam.php
• AdwCleaner:
  http://www.bleepingcomputer.com/download/adwcleaner/
  http://www.softpedia.com/get/Antivirus/Removal-Tools/AdwCleaner.shtml
• SuperAntispyware:
  http://www.superantispyware.com/
• Microsoft Safety Scanner:
  http://www.microsoft.com/security/scanner/en-us/default.aspx
• Windows Defender:
  http://windows.microsoft.com/en-us/windows/using-defender
• 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.

• Anti-rootkit utility TDSSKiller:
  http://support.kaspersky.com/5350?el=88446

See also:

• "Spyware on Windows": http://kb.mozillazine.org/Popups_not_blocked
• https://support.mozilla.org/kb/troubleshoot-firefox-issues-caused-malware

I guess there's some other program doing this, and it is only because FF is my default website that it does it in FF. Tried switching to another browser as default and it popped up that browser instead, even when FF is up and running.

Thank you guys.

That's a very good test. After all malware has been cleaned out using several tools, if the problem continues, there is one place left to look based on past threads: some malware adds items to the Windows Task Scheduler. It's somewhat challenging to sort through the entries, but you can take a look for anything with an unusual command line:

• Windows XP: Start button > [All] Programs > Accessories> System Tools > Scheduled Tasks

• Windows Vista/7: Start button > Control Panel > System and Security > Administrative Tools > Task Scheduler

• Windows 8: ?? You might try the charms bar search box if you don't find it in the control panel.

I found jscher2000's post "A redirect that occurs only at startup is difficult to catch using the Developer Tools." to be the most helpful. He suggests:

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

Then, instead of searching for link.o: (2) In the search box above the list, type or paste browser.newtab.url.

(3) Right click on browser.newtab.url and select reset. This will change it to the default value "about.newtab".

Hopefully this will resolve your issues. Thanks to jscher2000.

Found the malware at last, it is called Microsoft Windows. This problem was found about 2 years ago: https://answers.microsoft.com/en-us/ie/forum/ie10-windows_8/windows-8-goes-to-bing-by-itself-all-the-time/386e9a25-8149-4ee6-84b4-65332022c2a7?page=1&tm=1436444097124

Did virus and malware scans with multiple softwares and nothing showed up, so the only possible criminal is M$. (Seems like people got rid of the problem simply by uninstalling competitor softwares like Chrome and Firefox from their computers, figures.)

They even go so nice to disable my regedit rights,(I am the admin and only user on my computer) almost nothing works until I used the inf from Norton that was supposed to be used against viruses.

I hate M$

I've just had the same problem, it was probably brough to my pc along with an audio codec pack, in spite of being careful etc. I tried all the adware removal tools as described above but Bing still loaded with every new tab. I then tried using the Firefox menu (top right), the Help button/Troubleshooting Information/Refresh Firefox and thought it had done the trick but for no apparent reason I had no search or browsing abilities at all. What fixed it was a fresh download of Firefox (via IE) and a new install. After that all is fine: All search engines back and everything behaving.