This is in mediawiki.feedback module which is hosted in core.
A quick fix to load this spinner image protocol-relative. Should be replaced with CSS and a locally-hosted image.
$( '<div class="feedback-mode feedback-submitting" style="text-align:center;margin:3em 0;"></div>' ).append(
mw.msg( 'feedback-adding' ),
$( '<br/>' ),
- $( '<img src="http://upload.wikimedia.org/wikipedia/commons/4/42/Loading.gif" />' )
+ $( '<img src="//upload.wikimedia.org/wikipedia/commons/4/42/Loading.gif" />' )
),
$( '<div class="feedback-mode feedback-thanks" style="text-align:center;margin:1em"></div>' ).msg(
'feedback-thanks', _this.title.getNameText(), $feedbackPageLink.clone()