-moz-inline-box values for the CSS
display property are now considered deprecated and disabled by default in Firefox Nightly and early Beta/DevEdition. Assuming no major issues arise, these values will be removed from all the channels in the near future.
Note that other non-standard values for the
display property, including
-moz-inline-grid, have already been dropped with Firefox 62.
Update: These values have been removed with Firefox 64.