Check the connection settings.

• Tools > Options > Advanced > Network : Connection > Settings
• https://support.mozilla.org/kb/Options+window+-+Advanced+panel

If you do not need to use a proxy to connect to internet then try to select "No Proxy" if "Use the system proxy settings" or one of the others do not work properly.

See "Firefox connection settings":

• https://support.mozilla.org/kb/Firefox+cannot+load+websites+but+other+programs+can

Clear the cache and the cookies from websites that cause problems.

"Clear the Cache":

• Firefox/Tools > Options > Advanced > Network > Cached Web Content: "Clear Now"

"Remove Cookies" from sites causing problems:

• Firefox/Tools > Options > Privacy > Cookies: "Show Cookies"

Thanks - cor-el, but unfortunately, this didn't solve the problem. When I checked "no proxy" it could no longer find the server for my Hotmail page. I have since also had the problem on Google (and all the related sites: gmail, etc.). I was able to correct that problem by telling google my current location, under the assumption that it was misinterpreting the source of my IP address. The results of my virus scan did confirm a trojan. I have vaulted that now - but I have no way of knowing if that was the source of this problem, which continues. Screenshot included of what I see on sign-in pages, even though I am in New York.

To trojan could have caused this issue.

Try Firefox Safe Mode to see if the problem goes away. Safe Mode is a troubleshooting mode, which disables most add-ons.

(If you're not using it, switch to the Default theme.)

• You can open Firefox 4.0+ in Safe Mode by holding the Shift key when you open the Firefox desktop or Start menu shortcut.
• Or open the Help menu and click on the Restart with Add-ons Disabled... menu item while Firefox is running.

Once you get the pop-up, just select "'Start in Safe Mode"

If the issue is not present in Firefox Safe Mode, your problem is probably caused by an extension, and you need to figure out which one. Please follow the Troubleshoot extensions, themes and hardware acceleration issues to solve common Firefox problems article for that.

To exit the Firefox Safe Mode, just close Firefox and wait a few seconds before opening Firefox for normal use again.

By doing so, we can see if it is a Firefox issue or an issue with your computer.

I don't think that it is necessary to leave Firefox and that this issue will be resolved very quickly and effortlessly.

Thank you, Whiz.

Unfortunately, the problem was still present in safe mode, but it's nice to be chipping away at the possible causes. I've since installed Maxthon, in addition to Opera (already on my machine) to see if FF is the only affected browser, and that does appear to be the case. (It's XP and I don't bother to open IE). I'll welcome any suggestions on where to go next.

Do a malware check with some 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
• 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
• AdwCleaner:
  http://www.bleepingcomputer.com/download/adwcleaner/
  http://www.softpedia.com/get/Antivirus/Removal-Tools/AdwCleaner.shtml
• 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

Try to check your IP address:

• http://www.yougetsignal.com/tools/network-location/
• http://whatismyipaddress.com/
• http://browserspy.dk/ip.php

The Reset Firefox feature can fix many issues by restoring Firefox to its factory default state while saving your essential information. Note: This will cause you to lose any Extensions, Open websites, and some Preferences.

To Reset Firefox do the following:

1. Go to Firefox > Help > Troubleshooting Information.
2. Click the "Reset Firefox" button.
3. Firefox will close and reset. After Firefox is done, it will show a window with the information that is imported. Click Finish.
4. Firefox will open with all factory defaults applied.

Further information can be found in the Refresh Firefox - reset add-ons and settings article.

Please report back soon.

Could you check the language preference Firefox sends to websites?

Either:

• orange Firefox button (or Tools menu) > Options > Content > "Choose" button in the Languages section (added screen shot)

• the about:config preferences editor, intl.accept_languages preference (right-click > reset)

If this is the cause, it still leaves the mystery of what changed it...

You can also check the general.useragent.locale pref on the about:config page.

Thank you everyone, for your help. Sorry to have been away so long, but I needed to do a Full virus scan. The issue seems now to have been resolved - and there were several viruses found. It turns out that my virus scan schedule was turned off - so I have been only getting real-time scanning for who knows how long. I use Avast - and I suspect it was reset when I had to renew the license; an annual event.

In addendum - I need to mention that the problem was still there (just masked) on later attempts to access sites. Resetting Firefox solved the immediate problem. There was quite a lot of spyware and viruses happening - most acquired through the Guest user name that my kids use sometimes. I've had a good talk with them!