>>Does anyone know how to do this in context menu in a (any) browser?

This might help...

1. Write a script that you want to execute.

<SCRIPT LANGUAGE="JavaScript" defer>
  window.open("http://developer.ebay.com","","height=800,width=800,lef
+t=80,top=80,scrollbars=yes");
</SCRIPT>
[download]

2. Point to the script from your IE Menu Extensions. Here's an example of a generic installer (leveraging the excellent example from svsingh):

REGEDIT4

; Replace the following values with your own information.
;
; <INTERNAL AND DISPLAY NAME> = Name of the context menu item. 
;                  This will be seen in the navigation pane of the 
;                  registry editor AND in your IE context menu.
;                  Use alphanumeric chars. Spaces are OK.
; <PATH_AND_HTM_FILE> = The path to the script file.  Use double
;                   backslashes.  For example:
;                   C:\\IEScripts\\foo.htm

[HKEY_CURRENT_USER\Software\Microsoft\Internet Explorer\MenuExt\<INTER
+NAL AND DISPLAY NAME>]
@="file://<PATH_AND_HTM_FILE>"
[download]

See MSDN for additional options that control which context menus in which the item will appear, and how to set the DWORD in the above .reg file: About the Browser > Controlling the Context Menus.