Could you report back on its behavior in a little more detail? For example:

• If you click a link to site A do you get taken to site B instead? Are there particular sites where this happens, such as search engines?

• Does Firefox open this page or a new tab or new window even if you are not currently active in the browser? Or even if Firefox is closed?

Both of these can indicate malware of very different kinds.

For the second scenario, this recent thread might be relevant: Firefox keeps opening tabs on it's own whether I am on-line or not. I have reset several times and there are no pipe characters in the home page address..

No. Here is what happens, which made me first think it might be a virus. I'm not ruling out a virus, because I know sometimes scans miss things. But here is what happens: I'll be looking at a web page. I won't click on anything, nor will another window open. Then without warning the page I'm on will disappear, and there will be a page about some sort of online game, or game I can download etc. Another thing that makes me think it's a Firefox addon is the fact that it happened on another computer which is sync'd to the computer I'm on now. The last one it redirected me to was called "League of Angels" with a web address of passport(dot)game321(dot)com I would love to know what is causing this. It is very frustrating and to tell you the truth a bit scary to know that something can simply take over my browser like this. What if it can snoop on my keystrokes? What if it can get my personal info, like credit card numbers I've entered? Thank you so much in taking an interest in this. I appreciate any help you can give me.

Does the Back button work normally when this happens?

To better distinguish a possible external issue, could you force externally launched pages to open in a new window for the time being? Here's how:

In a new tab, type or paste about:config and press Enter. Click the button promising to be careful.

In the filter box, type or paste link.o and pause while the list is filtered.

These are the preferences of most interest (on the third one, please modify to the bolded item):

(A) browser.link.open_newwindow - for links in a Firefox tab that launch in a new window through the target attribute

3 = divert new window to a new tab (default) (checked*) 2 = allow link to open a new window (unchecked*) 1 = force new window into same tab

* First checkbox in Options > Tabs

(B) browser.link.open_newwindow.restriction - for links in Firefox tabs that launch new windows through JavaScript

0 = apply the setting under (A) to ALL new windows (even script windows) 2 = apply the setting under (A) to normal windows, but NOT to script windows with features (default) 1 = override the setting under (A) and always use new windows

(C) browser.link.open_newwindow.override.external - for links in other programs

-1 = apply the setting under (A) 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

After making this change, if the surprise page opens in a new window, most likely its source is external. If it continues to navigate the active tab, then an external source is unlikely.

Okay, I've done as you asked. Just to note it hasn't happened lately. Perhaps it was due to the Flashgot addon I deleted.

Oh, by the way, yes the back button works normally. That's how I've gotten out of all the times it has happened. I hope we can find out the problem.

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

Thank you for your help. I am definitely keeping the list you posted. For some reason, I can't download anything from the Internet. Either my ISP is having problems right now, or there's something going on deeper than just a redirected browser. At any rate, I'm performing another scan with my installed antivirus right now. I also ran an EICAR virus test, and my antivirus picked it up instantly. I can connect to webpages with no problem, but I get an error message every time I try to download a file. Weird...

Great suggestions. You can prevent most spyware/malware from even getting on your PC using this free program. Spywareblaster, it also has restricted sites settings.

https://www.brightfort.com/spywareblaster.html

good luck

Hi Deguisse, according to the Wikipedia article on SpywareBlaster, it blocks ActiveX controls. Since Firefox does not run ActiveX controls, this program would not be especially useful for preventing problems in Firefox.

http://en.wikipedia.org/wiki/SpywareBlaster

Hi jscher2000, True.

But, what about those cookies? Snapshots of your host file? Restricted sites?

And on occasion you must use IE (yuck) for those sites that do not like FF. Even if firefox doesn't use active-x it can still get hijacked. It is still a good idea to control your web. it is free app that has a proven track record w/myself and friends for over 8 yrs. Only reason i suggested it.

Hi Deguisse, yes, I hadn't noticed that SpywareBlaster adds cookie blocks for untrusted sites to Firefox. Its other benefits relate to other programs. I'm not saying it isn't valuable overall or worth checking out, but this particular program isn't going to help block malware from infecting Firefox.

Ok, I'll take my 1 or 2 pieces of spyware/malware a year and move on. Have a good day.

I leave my PC on most nights and Firefox is always redirected to an advert page sometime between 1am and 2am. One was for the Survey Scam reported elsewhere (https://support.mozilla.org/en-US/questions/996211) and another was an advert for Tunup Pro. They have denied any responsibility and suggested I disable add ins and install a pop up blocker. That has not worked.

Hi emperorbruce, try setting your default browser to IE or another browser before going to bed. If the unwanted pages open in the other browser, the problem most likely is external malware that launches a URL in your default browser.

To address that:

(1) Remove any unwanted software (2) Clean up any scheduled tasks

To start, I suggest opening the Windows Control Panel, Uninstall a Program. After the list loads, click the "Installed on" column heading to group the infections, I mean, additions, by date. This can help in smoking out undisclosed bundle items that snuck in with some software you agreed to install. Take out as much trash as possible here.

Next, you could try several malware scanners. Our support article lists tools other Firefox users have found helpful: Troubleshoot Firefox issues caused by malware. Note: those are free and take a while to run. If they terminate quickly and prompt you to buy, your computer has a serious infection.

To check the Windows Task Scheduler:

• 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.

Some past threads on the "dsite" problem:

• How can I keep Firefox from opening a window to website tofushopnews.com
• How do I get rid of sponsorship tabs that open automatically?