Ok, so this could be a Firefox bug, cuz I only seem to see it there, but here's what happens:
1. Firefox is on workspace 1, maximized, set to open links in new tabs.
2. Mail client is on workspace 2.
3. I click a URL in my mail client.
4. I use the keyboard shortcut (alt+ctrl+leftarrow) to switch back to workspace 1 OR I click the workspace in the pager.
5. Firefox, being the only app visible on the workspace at the time, is focused automatically.
6. Taskbar in panel shows Firefox with bold text, pulsing.
7. I click around the Firefox window; no change.
At this point I can get the flag to clear by one of the following:
1. Clicking on Firefox's window decorations (well, the title bar; borders aren't visible since the window is maximized).
2. Alt+tabbing to another window and then back.
3. Alt+tabbing to bring up the tabwin, but re-selecting Firefox without focusing another window.
xprop output verifies that _NET_WM_STATE is _NET_WM_STATE_DEMANDS_ATTENTION.
_NET_WM_ICON_GEOMETRY(CARDINAL) = 8, 0, 181, 20
window state: Normal
icon window: 0x0
_NET_WM_ALLOWED_ACTIONS(ATOM) = _NET_WM_ACTION_CLOSE, _NET_WM_ACTION_ABOVE, _NET_WM_ACTION_BELOW, _NET_WM_ACTION_FULLSCREEN, _NET_WM_ACTION_MOVE, _NET_WM_ACTION_RESIZE, _NET_WM_ACTION_MAXIMIZE_HORZ, _NET_WM_ACTION_MAXIMIZE_VERT, _NET_WM_ACTION_SHADE, _NET_WM_ACTION_MINIMIZE, _NET_WM_ACTION_CHANGE_DESKTOP, _NET_WM_ACTION_STICK
_NET_FRAME_EXTENTS(CARDINAL) = 3, 3, 21, 3
_NET_WM_DESKTOP(CARDINAL) = 0
_WIN_WORKSPACE(CARDINAL) = 0
_WIN_STATE(CARDINAL) = 0
_NET_WM_STATE(ATOM) = _NET_WM_STATE_DEMANDS_ATTENTION
Client accepts input or input focus: True
Initial state is Normal State.
bitmap id # to use for icon: 0x3200040
bitmap id # of mask for icon: 0x3200041
window id # of group leader: 0x3200001
WM_WINDOW_ROLE(STRING) = "browser"
XdndAware(ATOM) = BITMAP
_MOTIF_DRAG_RECEIVER_INFO(_MOTIF_DRAG_RECEIVER_INFO) = 0x42, 0x0, 0x5, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x10
_NET_WM_ICON(CARDINAL) = [elided]
_NET_WM_SYNC_REQUEST_COUNTER(CARDINAL) = 52428863
_NET_WM_WINDOW_TYPE(ATOM) = _NET_WM_WINDOW_TYPE_NORMAL
_NET_WM_USER_TIME_WINDOW(WINDOW): window id # 0x320003e
WM_CLIENT_LEADER(WINDOW): window id # 0x3200001
_NET_WM_PID(CARDINAL) = 13919
WM_LOCALE_NAME(STRING) = "en_US.utf8"
WM_CLIENT_MACHINE(STRING) = "kepler"
program specified minimum size: 0 by 0
window gravity: NorthWest
WM_PROTOCOLS(ATOM): protocols WM_DELETE_WINDOW, WM_TAKE_FOCUS, _NET_WM_PING, _NET_WM_SYNC_REQUEST
WM_CLASS(STRING) = "Navigator", "Firefox"
WM_ICON_NAME(STRING) = "Enter Bug: Xfce - Mozilla Firefox 3.5 Beta 4"
_NET_WM_ICON_NAME(UTF8_STRING) = 0x45, 0x6e, 0x74, 0x65, 0x72, 0x20, 0x42, 0x75, 0x67, 0x3a, 0x20, 0x58, 0x66, 0x63, 0x65, 0x20, 0x2d, 0x20, 0x4d, 0x6f, 0x7a, 0x69, 0x6c, 0x6c, 0x61, 0x20, 0x46, 0x69, 0x72, 0x65, 0x66, 0x6f, 0x78, 0x20, 0x33, 0x2e, 0x35, 0x20, 0x42, 0x65, 0x74, 0x61, 0x20, 0x34
WM_NAME(STRING) = "Enter Bug: Xfce - Mozilla Firefox 3.5 Beta 4"
_NET_WM_NAME(UTF8_STRING) = 0x45, 0x6e, 0x74, 0x65, 0x72, 0x20, 0x42, 0x75, 0x67, 0x3a, 0x20, 0x58, 0x66, 0x63, 0x65, 0x20, 0x2d, 0x20, 0x4d, 0x6f, 0x7a, 0x69, 0x6c, 0x6c, 0x61, 0x20, 0x46, 0x69, 0x72, 0x65, 0x66, 0x6f, 0x78, 0x20, 0x33, 0x2e, 0x35, 0x20, 0x42, 0x65, 0x74, 0x61, 0x20, 0x34
Allow me to say i have observed this bug to, tho the way i bump into it is by having focus stealing prevention on, hit a link in some other app while firefox is on the same workspace, click firefox, and watch the button flash as there now is a new tab inside the firefox window.
Notice that the firefox button only starts blinking for attention after firefox have gotten focus, not when a new tab is first opened inside it from a external source.
Just noticed that even if a new tab is added in another window, its the window that first gets focus that will be marked with attention.
i had two windows of firefox up on the same workspace, the second got a tab opened in it, i focused the first and it got the attention marker...