the new update 57.0.4(64 bit) carries a bug. i hit a new tab, and the taskbar shows a new window. chrome isn't showing up anything like this, so probably its an issue with firefox only. i use a windows8.1 64 bit system. problems are more while closing the application. i need to close every tab(better call it window) separately. Iam attaching a screenshot for more elaborations. you can see the windows overlook through taskbar shows the exact tabs on top of the screen. number of outlines of firefox in the taskbar used to represent the number of windows. till last week it used to be just one for multiple tabs on same window. but you can see now they are equal to number of tabs on the same window expecting a reply ASAP