Mouse is still a king on the desktop. But for some strange reason, with every new release, Firefox UI is less and less suitable for usage with mouse. Just to name a few recent issues:
Hiding scrolls, that a hard to find and grab, when you need them
Huge tabs and other UI elements. They are wasting screen space and do not add any additional comfort.
Browser is not friendly to a tipical mouse gestures. For example you need to click on an item in main menu, instead of just hovering over it. Tab overflow menu does not support drag and drop.
Menus have lost icons, which have been a great way to speed up navigation.
All of that should be fixed in default UI behavior, and touch friendly features moved to some special UI mode.
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