FFe: shipping globalmenu-extension by default

Binary package hint: firefox

We want to ship globalmenu-extension by default for Firefox users. This is an extension I've been working on that integrates Firefox with the global panel-menu in Unity, and the plan was that we would ship this in Natty but I just missed feature freeze.

This extension is already shipped by default for Thunderbird, and has been for several weeks. So far, no bugs have been reported for it (although it was affected by bug 723873 last week, but that is fixed now). I have also shipped this extension in my PPA since January, which people have been testing successfully. (I know people are testing it because there was a spike in crash reports submitted to http://crash-stats.mozilla.com/ due to this extension after I initially landed support for icons, but that was fixed quickly and there are no more crashes being submitted due to this). Several people on the desktop team have also been using this for several weeks.

I plan to build this from the Firefox source tree, like I do with Thunderbird. The reason for this is that it uses a lot of interfaces which might break in security updates, and building it from the Firefox source tree guarantees ABI compatibility.