If the shortcut is clean, then presumably it's something internal. If the home page address is correct through all this, then it's probably caused by a bad add-on.

Here's my suggested procedure for tracking down and cleaning up bad add-ons and other ad injectors. I know it seems long, but it's not that bad.

(1) Open 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. Be suspicious of everything you do not recognize/remember, as malware often uses important or innocent sounding names to discourage you from removing it. Take out as much trash as possible here.

(2) Open Firefox's Add-ons page using either:

• Ctrl+Shift+a
• "3-bar" menu button (or Tools menu) > Add-ons
• in the Windows "Run" dialog, type or paste
  firefox.exe "about:addons"

In the left column, click Plugins. Set nonessential and unrecognized plugins to "Never Activate".

In the left column, click Extensions. Then, if in doubt, disable (or Remove, if possible) unrecognized and unwanted extensions. Bear in mind that all extensions are optional, none come with Firefox, and you can learn more about them by checking their reviews on the Add-ons site.

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.

Any improvement?

(3) You can search for remaining issues with the scanning/cleaning tools listed in our support article: Troubleshoot Firefox issues caused by malware. These on-demand scanners are free and take considerable time to run. If they finish quickly and especially if they require payment, you may have a serious infection. I suggest the specialized forums listed in the article in that case.

Success?

(4) Check your connection setting here:

"3-bar" menu button (or Tools menu) > Options > Advanced

Click the Network mini-tab, then the "Settings" button. The default of "Use system proxy settings" should piggyback on your Windows/IE LAN setting, or you could try "No proxy" to see whether that helps.

By the way, it seems bing.vc is a site operated by Beijing MSYT Technology Co., and has no relationship with Bing from Microsoft.

In a thread on another forum, they had to go to extraordinary lengths to remove the malware that keeps modifying the system: http://forums.mozillazine.org/viewtopic.php?p=14290001#p14290001

The smart folks on the malware cleanup forums listed in our support article (see #3 above) might have a tool for it by now. I suggest linking to the above for reference if you post there.