598593 - Monitor switching with Ultramon causes rendering to be performed at wrong resolution

Status: UNCONFIRMED

(Firefox :: General, defect)

Description

[flanktwo]

User-Agent:       Mozilla/5.0 (Windows NT 6.1; WOW64; rv:2.0b6) Gecko/20100101 Firefox/4.0b6
Build Identifier: Mozilla/5.0 (Windows NT 6.1; WOW64; rv:2.0b6) Gecko/20100101 Firefox/4.0b6

I use Ultramon (http://www.realtimesoft.com/ultramon/ - free trial download) which adds a button to a window's title bar to move that window to another monitor. I have a laptop display (primary display) and an external monitor (secondary display). When Firefox 4 beta 6 is maximised on my primary display and I switch it to the external monitor, the window is moved but Firefox renders the window itself (i.e. title bar, tabs) and the web page at a lower resolution and then stretches it to fit the actual window size.

Reproducible: Always

Steps to Reproduce:
1. Install Ultramon
2. Maximise Firefox on primary display.
3. Use Ultramon's "move" button to move Firefox to external display.
4. Firefox now displays the same webpage but it appears to be firstly rendered at a lower-than-screen resolution, then stretched to fit the maximised Firefox window.
Actual Results:  
The entire Firefox window (including title bars) appears to have been stretched to cover the whole screen.

Expected Results:  
The Firefox window should not have been screen.

I am using the default Windows 7 theme.