User Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.11; rv:43.0) Gecko/20100101 Firefox/43.0 Build ID: 20151216175450 Steps to reproduce: 1. Ensure that three-finger tap is turned on in Trackpad settings on the computer. ("Look up & data detectors" should be checked). 2. Hover cursor over word in browser window opened to any webpage. 3. Tap trackpad with 3 fingers. My setup: Macbook Pro Retina 15-inch, Mid-2014 model Firefox 43.0.1., all add-ons disabled Actual results: No response. Expected results: Dictionary look-up, as in other OSX applications. See animation in System Preferences pane when three-finger tap is selected for a visual representation.

This is another duplicate of one of the current OS X top bugs: https://bugzilla.mozilla.org/show_bug.cgi?id=1212527 Since I can't set this to dupe, would be great if someone from Mozilla Firefox QA could do the honors...