I created a very simple module that adds a command to the Content Editor that allows the user to open any item from the content tree in a new browser window (or tab).
This functionality is for some reason not provided out of the box, other than the Preview command which opens an item in a new window but also in preview mode, which is not always desired.
This is what it looks like after installation:
Here is the GitHub repository for this module: https://github.com/ParTech/Browse-Command
You can download the Sitecore package directly from here: https://github.com/ParTech/Browse-Command/raw/master/Release/ParTech.Commands.Browse-1.0.0.zip
Use the Sitecore Installation Wizard to install that package. No extra configuration required.
Tested with Sitecore 6.5 and 6.6 (both latest revision), but I expect it to work from at least version 6.3.