webroot/rsrc/css/core/core.css defines -moz-outline-style: none.
This Mozilla-only CSS property was used only in Firefox <=1.5.
Firefox >=2 (released in 2006) supports the standard outline-style property: https://caniuse.com/?search=moz-outline-style
Current Firefox 116 does ignore -moz-outline-style: none so it has no value.
This CSS line should either be removed (targets Mozilla browsers only; cannot find any webkit etc equivalent), or it should be replaced with standard outline-style (which then would also be applied to non-Mozilla browsers).
The file above is the only appearance of the string outline-style in the entire Phorge codebase.
(In any case, when writing a patch make sure to also run bin/celerity map before submitting that patch for review.)