This Firefox Extension redirects all Bing search queries (e.g. from Cortana or the Visual Studio Debugger) to Google. The implementation is quite simple for now and may not be particularly robust.
If you want to be able to redirect search requests from Windows System (such as Cortana) you must have Edge Deflector already installed to redirect search queries from Edge to your default browser Firefox.
To install the extension download the latest release and open the .xpi file in Firefox.