Any link from AppleMail will open SeaMonkey (default browser). Two windows launch from clicking on the link. A blank window, then the window that displays the requested link on top of it. Happens every time. If I disable AdBlock in Add-Ons Manager, the problem immediately disappears. I've tried a bit unclicking some Ad Block display options, such as show in tool bar, the problem still persists. Mac 10.10.4, Desktop Mac Pro. SeaMonkey 2.3.8. AdBlock 18.104.22.168. I've turned off and on my other add-ons, one at a time: DOM inspector, FlagFox, NoScript. They did not affect problem behavior. I can stop the issue or start the issue at any time, simply by enabling or disabling AdBlock.