Ok, so I had two Firefox instances running, each with few tabs, one set regular, the other with private tabs. I was changing tabs and windows, it all stayed fine for 2 hours. I had two browser windows, win explorer window, Photoshop and some others Then , I opened one email from Groupy and new Groupy tab opened for that particular email and then I clicked on a URL in the email. I saw things happening, like a small window almost tried to open, I saw an URL at the top and was gone, at the end - new browser window did not open and 5 out of 6 regular browser tabs went blank...