Firefox rendering of certain Google Maps data now messed up

The symptoms below started in the last few days. I've also applied 1511 in the last few days. I can't say for sure whether the effect pre-dates the update or not since I hadn't used Maps much around that time.

Firefox 42.0 now shows the traffic overlay as broken pieces, and for certain broken lines like tunnels and railways it shows junk. This effect is worse with vertically-oriented lines, horizontal ones can look ok.

The image shows Edge on the left and Firefox on the right, showing the same area of Heathrow airport.


Of course this may be due to something else, but I've tried two versions of the graphic drivers (Intel 4600) with no change. I've also flushed the FF cache. Before I start changing everything I wondered if anyone else had seen something similar.

Further info: if I start FF in FF Safe Mode (i.e. shift and double click) it renders fine. However, in Safe Mode it shows the older representation, with 'Satellite' in the bottom left. In normal mode where it has the problem it shows 'Earth' at the bottom left so it would appear that the two modes are different anyway.

Over in the Google Maps group it would appear that somebody with Chrome is getting a very similar problem, so it may be Maps that is at fault here. Or Windows, or the graphic drivers, or something :)