I'm not sure I'm seeing the same thing exactly, but I have Firefox 35 and Workstation 11 installed on a Win-7 64 Host and I have an issue with user input pausing periodically when using Firefox.
I've noticed for some time that when using Firefox, I get 'pauses' of a second or so frequently while browsing. During the 'pauses', the ability to enter Mouse input (clicks, mouse wheel scroll, etc.) seems to 'stall' for a second or two. After a second or so, the Firefox display 'caches up' with the pending command and is o.k. until the next stall. Seems to happen/get worse with a lot of tabs open.
I eventually discovered that this 'input stall' seems to effect all input to Windows, not just the Firefox application. (So, clicking on something on the desktop also experiences a momentary delay as well when a pause is happening)..
The same thing doesn't seem to happen when using Internet Explorer, it only seems to happen when I'm running Firefox.
I've so far been unable to track the problem down. Since this happens when browsing with Firefox even when I'm not actively running Workstation 11, I didn't associate this as a Workstation/Firefox specific issue.
Not sure this is exactly what you are seeing, but I thought I'd throw this out in case it's similar.
