I don't have a solution but some information about the topic.
Roll your own browser: An embedding how-to - Gecko Redirect 1 | MDN[
^] explains old methods for embedding Firefox.
But using outdated methods which are not supported anymore or will not work in the future should be avoided. The above directs you to
XULRunner | MDN[
^]. But even that is not up-to-date.
As you can see there is actually no real support for embedding Mozilla. If you don't want to use IE you can use Chrome (
chromiumembedded / cef — Bitbucket[
^],
GitHub - lmsp/SimpleCEFDLL: Simple CEF( Chromium Embedded Framework ) DLL[
^] ) or have a look at Qt which provides the
Qt WebEngine 5.10[
^].
Finally you should think about using a recent Visual Studio version. They are free for personal use and even for small companies. So there is no need to use a 20 year old version from Windows 9x times.