Why not post in the MozillaZine Builds forum, where many pre-release "testers" hang out?

MozillaZine dates to ~2000, long before Mozilla had their own support fora, and long before Firefox came about.

http://forums.mozillazine.org/viewforum.php?f=23
You will need to register there to be able to post, but not for viewing threads. Check the threads labeled The Official Win32 201302## builds are out threads, which discuss problems and fixes in each days builds.

Whoops, just realized that you are running a 64-bit build of Nightly, which isn't currently being worked on. See if you have that issue in a 32-bit Build, preferably the 18.0.2 release version.

http://www.mozilla.org/en-US/firefox/fx/#desktop

Interesting, on a fresh install of 18.0.2 on a clean install of windows the issue is not present. Nor a fresh install of 21 64 bit.

It would seem at this point more likely to be something I screwed up in the about:config.

Edit: (This edit was made after my last post at 12:42 am)

I realize I sorta blew you off edmeister about those forums, I might go there and have a look, but I generally stay away from forums, they tend to be... well, not my type of place. And I thought I'd try the "official" support place first.

Actually it does somewhat seem to exhibit the same "unloading" behavior of the tabs after a period of time, but nowhere near as short as on my 64 bit install of nightly.

I would at this point really lean to some config option has been set much too low.

I think I understand the issue at this point, after messing with it a bit, I think it is a user environment issue, see I use 64 bit nightly because I tend to keep a lot of tabs open, when I say a lot, I mean at least 300 tabs minimum. So my nightly is always above 5GB memory, most I've seen is 10GB, but anyway, this behavior only seems to happen when I have all my tabs loaded and firefox is at a really large amount of memory usage, it seems to try and unload tabs right away, but when I restarted it and tried with no tabs loaded at all, the issue did not happen.

At this point I am trying to figure out which values actually affect how much memory firefox seems to think is too much and starts unloading things, I had just changed browser.cache.disk.capacity to 8388608 (8GB) to no real effect, trying browser.cache.memory.capacity to the same value right now, but it seems to do nothing.

Edit: (I didn't even realize you could edit posts)

Anyway, after further screwing around, I take back what I said, it seems to have nothing to do with the memory after all, but rather when I open up the tab groups page is what seems to trigger that behavior. What I did was close firefox down in a tab group with quite a few pages (at least 100) and then reopened it in that same tab group and waited for it to load all of the pages in that group, the memory usage was well over 4GB by the time it was done, and I tried opening the test images, much to my surprise, switching between them gave the desired result of them not really taking any time to re-scale themselves. I thought I'd mess around a bit more and opened up the tab group page to view my groups, went back into that tab group I started in, and sure enough the test images then displayed the behavior.

I really don't have any idea why tab groups would do this, but that is all I have now.