On occasion, the delete-button does not appear to list of actions, and therefore deleting of actions is not possible.

This seems to happen more or less irregularly, so can't really say what causes it Sometimes the problem disappears after quitting java (logout -> wait for java to die) and restarting, but sometimes that doesn't help either. In that case waiting for a random period of time might do the trick.

Don't know if this is a mac-issue, a specific firefox issue, or java8-issue. Or, after all these possibilities, maybe a neure-issue

Attached an image which shows how the action is not indented (in which case the deleting is not possible).