I... but... er...
This is probably the most ridiculous thing I've ever seen on this site.
You could write a two line C program that allocates all the memory on your system and then sits in a loop doing nothing, but then you'd be wasting even more electricity because your hdd would be reading/writing to your swap space. :|
> I'd rather have it used than have to fetch something from disk or the network.
Modern operating systems do use your free memory for cache. Linux will regularly chill at 90%+ memory usage (the majority being cache that can be freed instantly when other apps need it) and Windows has SuperFetch which does basically the same thing as I understand.
Yes modern OSes do use non-Application RAM for caching, mostly files and other small buffers. While Firefox is probably doing a lot of caching for web content, something that modern OSes don't yet do. Hence I have no qualms about it using over a gig of RAM.
I guess my comment was read more angrily than I meant it to sound. What I mean is let applications use as much RAM as they need and be done with it.
Then again do you actually notice a slow down when you try to edit those photos? Have you run benchmarks to see if it's really a problem with RAM usage or if it's some Flash or other plugin that's gobbling up your CPU, hence the slow down.
Does that really matter so much, since if you actually need to use that Physical ram for your editing task the OS should page out physical memory from the browser and other unused applications and make it available for your needs.
I've been working on large images in Gimp and Hugin/panotools in the past, and reached a point where swap was being used. The system immediately slowed to an unusable crawl with only a few % of swap in use. Considering that rotating hard drives have a random access throughput of a few MB/s, it's not surprising. These days a swap partition's only use is hibernating. Swap is effectively useless.
One webapp I'm working on triggered a bug in older versions of Chrome that caused it to grow rapidly in size, quickly consuming all of memory. Fortunately that was fixed.
So basically, I'd like to have another GB of image data in RAM before hitting swap (or whatever it is I'm working on), while still having my browser responsive.
Another thing to check would be what kind of ad ons you had installed, since I would imagine that they could have quite a significant impact on memory usage and performance.
I find it strange that people still think of RAM as a precious resource that needs to be conserved and under-utilised. I'd rather have it used than have to fetch something from disk or the network.