If you're simply looking to write the webpage with codes and be able to preview it in the application, NVU and Amaya both have this feature. You can see the preview in the preview tab and edit the webpage in either the source tab or the normal tab (NVU).
From what I can tell, you're looking for a program that allows you to write a webpage in html code and then preview it without opening firefox or internet explorer. Even if you're looking for a program that allows you to edit in normal mode and preview the webpage outside of a browser or just a program that will allow you to preview offline webpages outside of a browser NVU will do the job.
If you look at the bottom of this screenshot you'll see that NVU allows you to edit the webpage in Normal (WYSIWYG) Mode, HTML Mode and Source Mode. It also allows you to view a preview of the webpage from within the application. NVU will also allow you to edit the webpage(s) without codes in Normal Mode. This mode is basically like using a graphics/text editor to build the webpage, it allows you to create all sorts of html objects without knowing the specific html codes that are required to create them.
If you need help understanding the different modes of webpage editing and functions of HTML, here's a good resource:
You should consider taking the time to explain your wishes/problem in more detail in your first post. This will allow others to answer your question much quicker.