It's a very bad idea to move the screenshot function from the context menu in the address bar to a toolbar item you first have to position by customizing. This is exactly the kind of unnecessary interface change which annoys so many Firefox users. Okay, so why is it bad? Most "normal" users don't fiddle with interfaces, they accept it as it is. They expect functions they often use to stay in the same spot. If it's no longer there they think it's gone (and they're frustrated). They surely won't go looking for it in a customization menu. For me as a web designer the screenshot tool was extremely handy when dealing with clients, because it was very easy to explain where to find and how to use it, to send a screenshot of a website problem. Again, many common users don't know how to take screenshots with their system tools, so this was really helpful. Now, instead of explaining where to find it, I'll first have to explain how to customize the toolbar, what the item looks like, how to position it, etc. etc. The simplicity and helpfulness is gone. Suggestion: leave the screenshot function where it is by default, but offer the advanced users a way to make it a customizable item. Everyone is happy.

P.S. I only post this here, because the feedback site is currently deactivated.