I do not know if this bug was present in previous versions of FF.
When clicking on one of the menu items, it uses core-animated-pages with slide-from-right to change the view. This is working just fine in Chrome (both mobile and desktop). But in firefox, I get the previous and new view overlapping eachother for some time before the old view disappears, and there is no animation. I thought it could be related to me changing the order of the sections (in order to control if the view moves left or right), but then I tried the sample page:
http://www.polymer-project.org/components/core-animated-pages/demos/simple.html
On the sample page, slide-from-right does not work either in firefox. It changes instantly, and when you reach 5 and want to begin counting down again, it just hangs for quite a while.