Adjust Firefox user interface density to something more appropriate on desktop.
Use about:config
to alter browser.uidensity
option.
Set browser.uidensity
to `` to achieve normal user interface density.

Set browser.uidensity
to 1
to achieve compact user interface density.

Set browser.uidensity
to 2
to achieve touch user interface density.

The compact mode is so splendid that it makes me question the default options.
You can use GUI settings to alter this option, but it is always better to define default Firefox settings.