right side header not shown

hi, go into the monitor's settings and let it auto-adjust...

OK I am checking for monitor settings and I must be looking in the wrong place. I was looking in the control panel.

the monitor probably has some hardware-buttons - double-press the one saying AUTO in case it is present, or else take a look through the onscreen menu (or refer to its manual).

Philipp, Thanks. rebelflyer

Can you open the system menu via Alt+Space and resize the window with the keyboard?

Try to rename (or delete) the xulstore.json file in the Firefox profile folder.

You can use this button to go to the current Firefox profile folder:

• Help > Troubleshooting Information > Profile Directory: Show Folder (Linux: Open Directory; Mac: Show in Finder)
• http://kb.mozillazine.org/Profile_folder_-_Firefox