You could try using the Page info window. Go to a site you want to enable. ctl+i will get that window, go to its Permissions tab and for Open Pop-up Windows select Allow.

https://support.mozilla.org/en-US/kb/firefox-page-info-window

Thanks for your help @Terry. That worked :-)

You wouldn't happen to know how to stop Firefox from changing http to https on local addresses (192.168.xxx.xxx)?

Kind regards Pedro

You can try to enable HTTPS-Only mode and create an 'off' http:// exception for the exact IP address.

Thanks for your reply @cor-el. I have tried that, it doesn't work.

I have already posted this question "Stop Http redirecting to Https on local address", but no one has got a solution...

I have a suse tumbleweed os.

Kind regards Pedro.

Are you using Firefox from the Mozilla server as that version might behave differently ?

Is that IP address another device on your local network ? If so, does that server possibly support secure HTTPS, but has no valid certificate installed ?

Thank you for your reply @cor-el.

I don't know were it came from, it installed with Tumbleweed. Firefox Version 113.0.1 (64-bit).

Is that IP address another device on your local network ? - yes.

"If so, does that server possibly support secure HTTPS, but has no valid certificate installed ?" - (I assume when you say 'server' you are referring you to the device) - No, the device does not support https. No, the device does not have a certificate.

Kind regards Pedro