I have Firefox Quantum web-browser version 57.0.2 (64-bit) in Windows 7.
Sidebar, unfortunately, has a maximum width of about 540 pixels.
I tried to increase this constraint by going to
about:config and searching for "sidebar". Then I changed the setting devtools.toolbox.sidebar.width;500 to a value of 600. Then I restarted Firefox. But it did not work.
So how can I increase the maximum width of the sidebar?