Steps to reproduce:
1. Open at least two tabs
2. Right click on any page element and select Inspect Element (Q)
3. Click the Style button in the bottom right to show the style inspector window.
4. Switch to another tab.
5. Switch back to the original tab.
The style inspector window is blank. You may need to hover over the right corner to get the style window to re-appear.
The style inspector window displays what it was showing before switching tabs.
This appears to have gone away after recent changes to the style inspector.
Mozilla/5.0 (Windows NT 6.1; WOW64; rv:10.0a1) Gecko/20111106 Firefox/10.0a1
Bobby, thanks for your feedback.
verified on Mozilla/5.0 (Windows NT 6.1; rv:10.0a2) Gecko/20111218 Firefox/10.0a2