Ctrl + or - is a standard firefox setting to zoom/unzoom your window (it's also found on the View menu). That doesn't address the underlying issue that for a number of people, the standard display size has changed. I hate to be a stickler, but the display size needs to be correct when someone first comes into ATP. We regulars don't have a problem looking for and using work-arounds, but think of it from a brand new person's point of view.
I clicked here from a link on Google on Facebook or wherever, and while the site has this really nice crisp, clean look, it doesn't fill my monitor. First impressions matter, and that's not a good first impression.
OK, to be more precise: the home page mostly fills the monitor, and that's the actual first impression, but when you click into forums, they don't. Everything else that you click into from the top tabs (database/gardening ideas/lists, etc, including threads inside the forums) fills the screen with just that little white strip on the right, but I've clicked into the first 12 forums, and the display is consistently under-sized for the screen.
The profile page is another where the sizing is not consistent with the rest of the site.
The badges page, on the other hand, is fine
as is the "manage your profile" page and the "site preferences" page