From time to time (I don't know when, it seems to happen at random intervals), Unity starts getting confused about Firefox's window state. Below are the symptoms:-
1. Firefox, although maximized, no longer has its menu showing up when the pointer is over the Unity panel. Likewise, its window title no longer appears in the panel. When the Firefox window is focused and maximized, the panel is blank where the window buttons and menu or title should be, whether or not the pointer is hovering on the panel).
2. The Firefox icon on the Unity launcher shows a filled triangle on the right side, but an empty triangle on the left side, which seems to indicate that Firefox's window is focused, although not on the current workspace.
3. Alt+Tab orders Firefox's window to the back of the list (alt_tab_bias_viewport = true).
4. Alt+Grave over Firefox's icon causes Compiz to segfault (I should have gotten a stack trace; I'll do that next time).
5. Selecting Firefox's icon from Alt+Tab does nothing.
6. Clicking Firefox's launcher in the sidebar does nothing.
And here's the weird part: Other application switchers in Compiz, e.g. Ring switcher, and Scale, work as expected. Scale even properly detects the workspace that Firefox is on, judging from the [N] suffix to Firefox window's title. This indicates that the bug is probably not in compiz, but in Unity or something it uses.
All of the above symptoms are for one issue. The symptoms either appear all at once, or not at all. The only way to get rid of this seems to be to restart Unity or the application in question (Firefox)
ii firefox-trunk 10.0~a1~hg20111018r78888-0ubuntu1~umd3 Safe and easy web browser from Mozilla
ii unity 4.24.0-0ubuntu2 Interface designed for efficiency of space and interaction.
DistroRelease: Ubuntu 11.10
Package: unity 4.24.0-0ubuntu2
Uname: Linux 3.0.4-ck1-hyper1 x86_64
Date: Thu Oct 20 10:46:43 2011
UpgradeStatus: Upgraded to oneiric on 2011-10-14 (6 days ago)