Does it keep showing up as your home page:

1. immediately after changing it, it changes back
2. after you shut down Firefox and start it up again
3. even after fixing your home page setting, it shows up when you use the Firefox icon to start Firefox

You probably need to remove some software from the Windows Control Panel. Open Uninstall a Program and click the "Installed on" column heading to group by date. Look for unrecognized or suspicious programs that may have been part of a bundle. In another thread Proxy Tool was mentioned as related to V9.

For #1, the program Search Protect can block you from saving changes. When you are in the Control Panel, look for that one, too.

For #2, please see this support article: How to fix preferences that won't save. Also, utility programs like Advanced SystemCare may undo settings changes. You may need to turn off Surfing Protection, Home Page protection, and similar features in order to be able to clean up your settings.

For #3, check for a hijacked shortcut. right-click your Firefox icon > Properties. On the Shortcut tab, the Target should be no more and no less than the following:

"C:\Program Files (x86)\Mozilla Firefox\firefox.exe"

Also, you can mop up with some of the scanning/cleaning tools in our support article: Troubleshoot Firefox issues caused by malware.

Finally, if other Firefox features are affected, such as the new tab page, please post back for steps to clean those up as well.

I skipped over something, which is checking your extensions. Often the cleanup tools miss those. Try this:

Disable ALL nonessential or unrecognized extensions on the Add-ons page. Either:

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

In the left column, click Extensions. Then, if in doubt, disable (or if trashy, remove).

Usually 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.

Hope this helps.