Resize your Firefox window with one click
Say you want to create a bookmark or a bookmarklet for your toolbar that will let you resize your browser window. Just right click on your toolbar and select "New Bookmark."
Change the numbers to set your default resolution. Now you can easily switch between full screen and windowed mode at the click of a button. If you want to see how a website looks at different screen resolutions, you can create a series of these bookmarks.
What other Firefox settings adjustments would you automate by creating a bookmark?