Middle Click To Go Back

Go back with your middle mouse button.Default actions stay as usual.
You can still "open the link in new tab" or "close tab" with middle-click.
(and in linux, you can still paste with middle-click.)

But now:
* Click middle mouse button on an empty space on a web page to go back.
* Middle-click closes the current tab if no page to go back. (Optional)

----

Tested on WINDOWS and LINUX.

----

For Firefox: https://addons.mozilla.org/en-US/firefox/addon/5938

----

RELEASE NOTES
1.8
Works on "tabless windows", too.
1.7
Optional "middle-click closes the current tab if no page to go back" behavior looks like working :)
1.6.3.3
bugfix
1.6.3
onclick change to mouseup to overcome http://www.crbug.com/56124
1.6.2
Optional "Middle-click closes the current tab if no page to go back" feature does not close the browser anymore.
1.6.1
Options added to enable/disable "Middle-click closes the current tab if no page to go back."
1.6
Middle-click closes the current tab if no page to go back.
1.5
Works on Windows, too.
1.4
more responsive
more stable
1.3.1
added: "all_frames": true, to manifest
added: icons