Does the Bing page open instead of your previous session's windows and tabs, or in addition to them?

Here are some things to check that could override your settings:

(1) External software

Try using the Windows Control Panel > Programs and Features > Uninstall a program to view your recently installed software by date. This may bring to your attention an unexpected program that was installed along with something "free".

(2) Check your extensions.

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

• Ctrl+Shift+a
• orange Firefox button (or Tools menu) > Add-ons

In the left column, click Extensions. Then, if in doubt, disable.

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.

(3) Check for a user.js file, which could be overriding your settings when Firefox starts up.

This article has the steps for that: How to fix preferences that won't save.

(4) Check the shortcut you use to start Firefox, to see whether the unwanted URL was inserted there.

Right-click the shortcut > Properties > Shortcut tab.

On the line that says target, the last thing should be firefox.exe" If you find anything following that, such as the address of the unwanted site, go ahead and remove it.

Does that help get Firefox to start up right?

Which security software (firewall, anti-virus) do you have?

Just windows protecter

Did you try jscher2000's suggestions yet.

You may also want to search for a conduit plugin as that is considered malware.

SEE: https://support.mozilla.org/en-US/questions/971707 and https://support.mozilla.org/questions/974780 for help