fire_me said

Could any other of the standard addons cause this?

Hi fire_me, thank you for sharing your extensions list. I'm not familiar with many of them. The key question is whether they block any content or not.

As a test, how about trying the search site in Firefox's Safe Mode? In its Safe Mode, Firefox temporarily deactivates extensions, hardware acceleration, any userChrome.css/userContent.css files, and some other advanced features to help you assess whether these are causing the problem.

If Firefox is not running: Hold down the Shift key when starting Firefox. (On Mac, hold down the option/alt key instead of the Shift key.)

If Firefox is running: You can restart Firefox in Safe Mode using either:

• "3-bar" menu button > "?" Help button > Restart with Add-ons Disabled
• (menu bar) Help menu > Restart with Add-ons Disabled

and OK the restart.

Both scenarios: A small dialog should appear. Click "Start in Safe Mode" (not Refresh).

Any difference?

Without the addons it works. The thing is, I alreay whitelistet/switched off the ones I suspected, Smart https, decentraleyes, Smart Referrer, but it didn't change a thing. I guess it would now be deactivating one after the other to see where it makes a difference?

Found it - it's smart https. Any ideas what to do to keep smart https?

Wait - it's not! It seems to be the windscribe addon - even when I don't use the VPN. Any ideas?

I notice its title on the Add-ons site is "Windscribe - Free VPN and Ad Blocker" so perhaps the Ad Blocker part is independent of the VPN part.

Looks like you can turn that off: https://addons.cdn.mozilla.net/user-media/previews/full/173/173072.png?modified=1543520606

BINGO! Thank you so much - sharp eye! works like a charm!