Is there a keyboard shortcut for "Paste & Go" in Firefox?

You can always WRITE your own shortcut with autohotkey.

Download and install Autohotkey. Implement this script:

;This will create for Windows+G combination

    #g::
    SetTitleMatchMode 2
    IfWinActive, firefox
    {
    Send ^L
    Send ^v
    Send {Enter}
    }
    return

A modified version of Paste and Go2 is available. To install it you have to go through some steps if you have the latest version of Firefox. Download the .xpi extension file on your system wherever you want to and now follow these steps.

1. Extract (unzip) the .xpi file. It is simply a zipped file with an .xpi extension, so you should be able to use something like unzip or Stuffit-expander (on Mac) to extract it.

2. Open the "install.rdf" file with a text editor such as Notepad. Find a tagline like this showing the "maxVersion" number (in this case 2.0, but it may differ depending on the extension):

   <em:maxVersion>2.0</em:maxVersion>

3. Change the "2.0" to "3.0.*" or whatever you need (the * covers any minor updates to release versions). That tells the installer that the version can be installed with the corresponding version number of Firefox or Thunderbird.

4. Save the changes you made to the install.rdf file.

5. Create a zip archive containing all the files that were in the original .xpi file, including your modified install.rdf file. Rename it to "myExt.xpi" or whatever you like. The crucial thing here is to use ".xpi" for the file extension.

6. Strongly recommended: before installing the extension, make a temporary backup of your profile folder or at least of the "extensions" folder inside your profile folder, which contains the installed extensions. That way, if something goes wrong, you can revert the changes easily.

7. Finally, install the extension: open the .xpi file from Firefox and it should install to install it via the "File → OpenFile" menu and select the .xpi file means the extension which you have downloaded.

If you don't want to follow this procedure then you can use disable the compatibility checker extension.

For more information about how to add FF extension via File menu see my another answer.

As you can seee in the image I'm using Ctrl+V for Paste&Go with open in new tab in background you have your choice.

Paste and go is up since release of FF4, right click on address bar "paste & go".. there are no keyboard shortcuts for the simple reason isn't needed, to press F6 (addressbar focus +select all), CTRL-V (paste), Enter (go) is faster than many other things shortcutted