You seem to have three problems that are not related:

$inhalt does not contain, the filled fields e.g. message with Hello . There is only 1 form on the side. Why are the fields not filled ?

This is because the content method is and stays the original content as returned from the webserver. You might or might not want HTML::FillInForm to populate the content with some more values.

2. Like to open firefox with the filled form.
3. I looked at HTML::Display module, but the simple example

Like I wrote to somebody just yesterday in an email, that's likely just not possible under Windows unless you write some code that makes HTML::Display use temp files that have a .html extension.

I'd like to use firefox instead. If I try to open the real webside it starts loading with IE but then breaks.

That's a very common yet entirely unhelpful error diagnostic. Unless you're talking about porcelain or wood, you need to be more specific about what breaks and how. In the mail I sent yesterday to some person, I mentioned the location parameter which sets the base attribute of the HTML. Maybe the page tries to access some "local" resources like JavaScript scripts or images, which need the URL of the originating page. Which is what the location parameter should be set to.