jdownloader captcha window doesnt open firefox browser - issue with dietpi?

hello, there is a jdownloader 2 app for downloads. on some hosters it opens captcha notes where I can click on open browser
where I should solve the captcha. but the browser never opens.

I am using DietPi 8.12 on Rpi4 with Xfce Desktop GUI (yes I know ^^) and firefox-esr was installed automatically.
I have not installed another browser and firefox is set to standardbrowser.

my question, could dietpi have an issue with that, so that something catching the jdownloader to browser handover?

DietPi are just a collection of shell scripts on top of a Raspberry OS. Desktop as well as browser are installed from official apt package source. Did you tried to use Chromium? Maybe there is a setting in Firefox blocking to open popup windows?

perfect, thanks! with Chromium it works!