Cannot edit Prioritized Labels (issues) with FireFox

GitLab CE: 9.3.0 (and prior versions)

Once a label has been prioritized (starred) it cannot be edited or deleted using Mozilla FireFox (tested on v54, Ubuntu). Mouse clicks are intercepted as drag/drop re-ordering.

The only work-around seems to be to un-star the issue, then edit it, then star it again.

Editing of Prioritized Labels works fine in Chrome.