They can be, but the more general answer is "Not Really" (the webpage would be displayed, but be difficult to use).
There are two main issues. Firstly, you need a headset with enough resolution to be able to read the text on the webpages easily. I'm a Rift S user which would struggle in this respect. I've not used a Reverb G2, but from wha I hear, it would probably be OK in this respect.
Secondly there is the issue of controlling the webpage. Windows gives one application at a time "Focus". The application in Focus receives input such as your keyboard/mouse input. As such when you are flying ED, ED has the focus. To use the web browser, it would need the focus. You'd need to be able to type onto the webpage, and use the mouse on it. ED would lose focus as whilst you are controlling the browser. You could get around the focus issue by making the projected window, a remote desktop of a second computer. (which runs the web browser) You still have the issue of typing blind, however...
As millgna says, overlays are great for viewing media.