You can do this probably by using a browser inside of easy-debian. I use this method to get larger virtual resolution for desktop apps. I do the following. 1. Install easy-debian. 2. inside easy-debian you can apt-get tightvncserver (something like that). then you can launch a vnc server at larger resolution. you do not need to be in LXDE. Opening an easy-debian shell is enough. 3. launch a vnc server like "vncserver :1". give it a password on first launch. 4. install vnc-viewer. 4. connect vnc to localhost:1.

You should now be able to launch iceweasel with a larger resolution.

if you have problems with CAPS then disable auto caps in text input settings. This seems to be an issue with vnc viewer.