Flash player problems

The reason that its launching Internet Explorer is that it's the default browser on your computer.  It's terrible, but there's no good way for the installer to know that you initiated the installation from a browser that wasn't the default.  It's a weird experience, and I've complained about it a lot over the years.  I totally get the confusion, but it's not really a problem that you need to worry about.

So, you've installed Flash Player on Firefox and it's not working.  It successfully installed, because you got the completion screen (even though it was in the wrong browser), but most of the major US browser block Flash Player from running by default at this point.  The websites you visit all do their own detection, and when they don't see Flash Player, many will incorrectly assume that it's not installed, since that was the way things worked until a year or two ago.

You probably just need to Enable Flash Player in your browser at this point.

Check out the following guide:

Flash Player Help