Could be a bad add-on. Here's my suggested procedure for tracking down and removing them. 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. Don't be fooled by seemingly innocent or important names if you do not remember choosing to install them. 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. (Note: you might not be able to manually Disable extensions in Safe Mode because they are disabled automatically.)

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?

If you are browsing from China, it could be something else, according to various discussions around the internet:

Any websites that have that use the Facebook Connect sdk cause the user to automatically redirect to wpkg.org

https://codeandcommand.wordpress.com/2015/04/26/wpkg-org-currently-undergoing-possible-attack-from-great-firewall-of-china-via-codeandcommand-com/ citing http://www.reddit.com/r/China/comments/33wpk3/anyone_else_almost_all_websites_in_both_chrome/

You can block facebook.net using the YesScript extension: https://addons.mozilla.org/firefox/addon/yesscript/ -- that will block the Facebook Like button from appearing on other sites, but if you aren't a big user of it, that's probably just fine with you.

If the above doesn't help and this only affects Firefox and not other browsers on your computer or your network, could you double-check your Firefox connection setting here:

"3-bar" menu button (or Tools menu) > Options > Advanced > Network mini-tab > "Settings" button

The default "Use system proxy settings" should piggyback on your Windows/IE "LAN" settings. But you can try "No proxy" to see whether that makes any difference.