I don't use Firefox very often. Generally I'm in Chrome or IE. But, I keep Firefox on my taskbar, because I do enough web development that it's prudent for browser compatibility testing.
Every now and then I get this dialog:
Note that when I'm not taking a screenshot, that first item has a blue highlight instead of gray.
What's the problem?
Well, first of all, it's a popup. It has its own window, which in my mind, means that Firefox thinks I ought to do something about it. The only action that appears to be there is the "Find Updates" button; but of course, that doesn't find updates to the plugin I just installed, which is the purpose of the dialog in the first place, isn't it?
No. In the screenshot, the Java Console 6.0.27 is the newly-installed plugin because I just installed Java (with MonoTouch and MonoDevelop).
Mozilla, this dialog sucks, and has sucked since I saw it back in the early days of Firefox. Take a lesson from IE, and if you want to show me a notification, put it in a bar. Make it say, "The 'Java Console' add-on has been newly installed." Or, "4 new add-ons have been installed; click here to see this list."
At the heart of this problem, though, is a cultural difference; I strongly believe that the *nix culture is reflected in this user experience. It was as if someone said, "OK, well, we'll run firefox --check-plugin-updates | firefox-ui and the result was piped to a new window, because it had nowhere better to go.
That's not to say that command-line piping to the UI is a bad thing (though I believe that it's better to make the programmatic interface between two subsystems, well, programmatic, not text), but if someone had actually spent some time designing the user interaction for the "New plugins installed" use-case, they would not have decided to simply reuse the "Show all installed plugins" UI.