We have version 1.1.1 of the JIRA plugin installed and it is causing problems with JIRA version 6.3.5.
I am a web developer myself and was able to investigate the cause of the error, and found that it was because in what looks like the initialisation code for the Ephor JIRA plugin, you are trying to trigger an event, JIRA.Events.INLINE_EDIT_BLURRED that is not defined for the version of JIRA that we are running. Thus, when trying to access the type property from the event variable, which is undefined, JS errors are being generated.
I have included a screenshot that shows the offending line highlighted, along with the tooltip that confirms that JIRA.Events.INLINE_EDIT_BLURRED is indeed undefined.
I know this appears to contradict some documentation that appears to be out of date, but it is definitely causing problems for us.
If nothing else, I would add a guard condition around the call to JIRA.trigger() so if that event does not exist, you don't try to trigger it. You may wish to go further, though, since that whole click handler for body seems unnecessary if you cannot trigger that event.
Let me know if you need any further info.