Firefox does not come with the Bing toolbar. Another program you installed bundled the Bing toolbar and added it to Firefox.

If you can locate the Bing Toolbar in Add/Remove Programs, uninstall it from there.

Otherwise locate the toolbar in Tools -> Add-ons -> Extensions from the Firefox menu bar, and uninstall or disable it.

It may be named Search Assistant or Search Toolbar 1.04.

See this thread for other possibilities: https://support.mozilla.com/en-US/forum/1/531033

If you use Help -> Troubleshooting Information, and the Copy all to clipboard button to paste the troubleshooting info here, I can help you identify the culprit.

Thank you thank you thank you.... i tried everything before this, could not find it in remove programs and many websites couldn't help. When i found this, it was soooo simple and accurate, i thought i was going to have to restore my computer and lose some work. Fabulous, i am sooo happy, thank you again.!!!

You ROCK! I went into my downloads and spotted Search Toolbar and immediately uninstalled it. All problems solved. Bing is GONE.

This add-on was installed without my permission when I ran an installer for another program. Also, it appears in the add-ons list with only two options: Enable and Disable. Uninstall is greyed out. I think add-ons should not be required to include uninstall functionality accessible from this menu. Is there any way such a requirement could be enforced?