What happens when you right click on this page? see screenshot

What OS? What Desktop? X11 or Wayland?

Try downloading Firefox from Mozilla, run firefox-bin from the folder and see if you have the same issue. https://www.mozilla.org/en-US/firefox/all/#product-desktop-release

Operating System: openSUSE Tumbleweed 20240524 KDE Plasma Version: 6.0.4 KDE Frameworks Version: 6.2.0 Qt Version: 6.7.0 Kernel Version: 6.9.1-1-default (64-bit) Graphics Platform: X11 Processors: 16 × AMD Ryzen 7 5825U with Radeon Graphics Memory: 62.1 GiB of RAM Graphics Processor: AMD Radeon Graphics Manufacturer: HP Product Name: HP ProBook 455 15.6 inch G9 Notebook PC

It depends on mouse cursor position when I do right click. Also screen resolution and site zoom / font size may play the part. That is why I thought I could have it fixed by applying some css.

Firefox 126 Flatpak installation. Operating System: Manjaro Linux KDE Plasma Version: 6.0.4 KDE Frameworks Version: 6.1.0 Qt Version: 6.7.0 Kernel Version: 6.6.30-2-MANJARO (64-bit) Graphics Platform: Wayland

Looks like you have more options than normal in you right click menu. Help me understand how this is a browser issue. Did you try Firefox in Troubleshoot Mode? https://support.mozilla.org/en-US/kb/diagnose-firefox-issues-using-troubleshoot-mode#search104

I tried a new profile and it works ok but in the new profile I don't have add-ons installed and css. Perhaps I need to investigate it further but if there was a css to make it "my way" it would work as a workaround.

Looks like you solved your issue. You can use sync to get your data in the new profile and see if it's the add-ons or css causing the issue.

https://support.mozilla.org/en-US/kb/how-do-i-set-sync-my-computer https://support.mozilla.org/en-US/kb/how-do-i-choose-what-information-sync-firefox