-moz-transition syntax was only supported from Firefox 4 to Firefox 15 according to https://web.archive.org/web/20130827073113/https://developer.mozilla.org/en-US/docs/Web/CSS/transition.

Per https://web.archive.org/web/20130827073113/https://developer.mozilla.org/en-US/docs/Web/CSS/transition and https://caniuse.com/mdn-css_properties_transition, standard transition has been supported since Firefox 16 released 08/2012.

Per https://developer.mozilla.org/en-US/docs/Web/CSS/Mozilla_Extensions, -moz-transition is not supported anymore and https://developer.mozilla.org/en-US/docs/Web/CSS/transition should be used.

Read CSS docs. Probably install ancient browser versions if you don't trust documentation. Try https://jigsaw.w3.org/css-validator/ and don't spot issues.