(Some) Bing (formerly Multimedia) maps won't open properly

Question

I am trying to access the maps associated with the names on the list of plaques at:
http://www.bristol.gov.uk/page/list-blue-plaques-bristol
on a computer running Windows Vista Home Premium and AVG Internet Security 2011.
Many of the maps have an overlay indicating the position of the plaque and giving the position of the plaque and names and distances from railway stations (see Ernest Bevin, the second name on the list). However, some of the maps do not have such an overlay (see Eric Ball, first name on the list).
When I try to open the maps using Firefox 7, I find that those without an overlay open without any problem, while those that have an overlay close immediately - in the blink of an eye, so to speak - and this problem persists even when all add-ons and plug-ins are disabled. However, if I try using IE 9, all the maps open without any difficulty.
This would suggest that the problem is somehow due to Firefox, but the puzzling thing is that my wife's laptop, also running Windows Vista and AVG, will open all these maps in Firefox without any problem at all.
Can anyone suggest why this might be happening?

Answer 1

Also: Setting the Finder to always open folders in a new window DID fix this, but I'd rather not do that if I can avoid it.