Pixlr is a free and probably the best web based image editor. I will show you how to open and and resize an image, I'm sure you will be impressed how well the web app actually works.
If you experience an Mac OS X program to freeze and you cannot exit it by clicking quit or using a keyboard shortcut, you can always force it to quit using the Activity Monitor.
Many times I find myself with a large number of opened tabs in Firefox browsers and thankfully you don't need to close the program in order to close all the tabs except the one I want to keep.
