The first goal of this patch was to remove the tabindex because it helps
to improve overall a11y. That led to move some html elements associated
with the buttons which helped to position these elements relatively to their
buttons.
Consequently it was easy to change the toolbar height (configurable in Firefox
with the pref browser.uidensity): it's the second goal of this patch.
For a11y reasons we want to be able to change the height of the toolbar to make
the buttons larger.
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