I am unaware any such possibility for Firefox, but others can confirm.
Assuming no possibility at the moment, your best alternative or workaround would be to execute the code for Firefox to run normally but invoke a breakpoint at some desired point of the test/automation, and do your debugging starting from there, your debugging from then on can be done interactively in shell like environment for languages that support it (e.g. python, Java), if you started it in a script/shell/CLI like fashion and invoke a breakpoint that would return you to the language's interpreter where you can continue to manually execute Selenium WebDriver API calls from the language as well as other code in the language.
But given your specified environment, I'm not sure whether you can do that breakpoint into interpreter shell technique for VB and .NET 8, hopefully you can. Otherwise, maybe closest technique might be to try with PowerShell or IronPython with WebDriver.