Per comment bug 1146777 comment 2. BugzillaJS also uses light boxes for any link to something that looks like an image (currently, URLS ending with (jpg|gif|png) ). And people have been requesting to link to use light boxes for more https://github.com/gkoberger/BugzillaJS/issues/97
IMPORTANT: this must be optional if implemented. The BugzillaJS feature is the bane of those of us dealing with crash and security bugs, where the links and attachments are examples of the bug in action. My life is miserable with that setting, but thankfully in BugzillaJS it can be turned off. I acknowledge that if it didn't crash me all the time, it's kind of nice to be able to see screenshots etc in-line for a normal bug.