A few versions back, Firefox (Mozilla as a whole) dropped support for its original method of supporting CSS3 rounded corners (border radius). Previously it needed the -moz prefix – -moz-border-radius
Starting in Firefox version 13, Firefox no longer honors the -moz prefix in respect to border-radius.
One solution is simply to remove the -moz prefix. You can do this via find and replace – find: -moz-border-radius and replace it with: border-radius
This will cause older Mozilla browsers to not display border-radius anymore. So you could also add just border-radius as an additional rule.
Support for the prefix was removed in Gecko 13.0 (Firefox 13.0 / Thunderbird 13.0 / SeaMonkey 2.10).