Its past time to have "device control" selection for Firefox users.
In Settings, allow a "device selection" which will optimize all Mozilla use.
That is "Select" smart phone, laptop, widescreen, etc. Then Firefox while shift settings to BEST use the available space on the user's device. The current approach is very, very space wasting.
Drop-down menus (bookmarks, applications, etc) need to be single spaced on 90% of devices.
Even this idea comment box has double spaced my idea. IF program designers believe double spacing is the future... why not make it triple or quadruple spacing and really make it dysfunctional? Spacing should always be "User Set" to conform ti the device being used.