HTTP request monitor and editor
It is extremely useful to monitor the traffic that's going thru the wire if something is not what expected by the web developer. Usually, I'm using Fiddler2 on a Windows machine, but I think, it would be absolutely great to... - optionally monitor all or filtered (by URL? host name? regex?) HTTP/HTTPS requests of a tab - edit/tamper HTTP/HTTPS requests - re-issue HTTP/HTTPS requests ... without additional software. That helps a web developer to debug i.e. an AJAX powered page or a remote server API.