Physical Memory Usage anomaly

Hope I'm asking in the right section.

Normally I might consider this a good thing, but it happened absolutely out of nowhere and I'm not sure what's up

Normally My physical memory usage sits around 40-45 when I'm doing everyday things like typing up this thread, around 35% if idling.

But just today, out of nowhere, My physical memory usage took a huge dip, right now it's at 27%, dropping down to 20% if idling. I have no Idea why.

I looked at the memory usage of all my programs, and many of them are only at about half what they use to be. For example, Explorer use to sit at around 35,000 k, and now it's down to 17,000 k.

I restarted and everything seemed to be back the way it was for awhile, when it suddenly all dropped again, still no idea why

So, what exactly is happening? Am I looking a gift horse in the mouth here, or should I be concerned?

I'm using Windows 7 on an HP notebook, didn't install any updates recently, to my knowledge. I actually have windows updated switched off for the time being

 

Ah, I found the trigger

Sometimes when I google image search something on Firefox, Firefox's memory usage rockets out of control and it crashes, it looks like everything else is slowing down to compensate.

Looking it up, Firefox likes to do this to people.