Flexbox model will replace old xul box as the default display model so
this patch adds support for that in a whole bunch of styles.
A lot of style rules are marked as "Fx < 112 compatibility" rules and
those can be removed when 112 hits release.
This patch makes focused urlbar overlay other toolbar instead of being
constrained to urlbar-container width. This also disables that weird
bookmarks toolbar margin by default, but leaves code for Firefox <108
compatibility. Unpinned tabs are now visible by default but that can be
reversed by setting a pref. And lastly this disables tabs
arrowwscrollbox css containment which would cause the style to not work
in Firefox 108.
