The ProcessWire module "ProcessPreview" is sponsored by dreizunull.com.
This module adds a "preview" button to a page your editing. After clicking it a preview of the changes will appear and a new window/tab.
After a long time I got the chance to start fixing bugs and improve the module.
I did a huge change in how the module works (only backend stuff - stays the same for the user). It should finally work with all systems and all templates.