Another bit of the story has emerged. I don't know why I did not notice this previously. It seems that Firefox is having difficulty working out which of its windows is on top!
I have now noticed that when a Firefox window is apparently rejecting keyboard input the text sometimes goes into another window, though the result may be invisible. It is only visible if the window that grabs focus has a text input box e.g. a search box (opened by Ctrl-F in FF), or if I had previously clicked in its address bar. I have not been able to detect a pattern behind the occurrence of this 'theft' of focus. I did not notice it previously because with large numbers of FF windows in a workspace (most of them minimised) I have to do an explicit search to see which window has accepted the input and sometimes there's no evidence because the focus was in the main part of the window, which does nothing visible with text input. (There may have been a text search triggered, but without leaving any visible record.) Sometimes the evidence is destroyed because I try typing in another window which accepts input, but wasn't previously grabbing the text. I haven't found evidence that text is going to a non-current tab, but I've never tried searching through all the tabs. Anyhow, it looks as if FF can tell which window is on top if I move in and out of a workspace, or if I 'open' a short-cut button for editing, but can get confused about which is on top if I minimise and maximise windows. My most recent experiment with a window (WinA) not accepting text is to partially cover it wtih another window (WinB) and then click on WinA's title bar to raise it. That always seems to put focus back in the raised window as expected, when merely opening the window from a minimised state does not. I have no experience writing window manager code, but I would have thought that when all windows are rectangular it should be easy to determine whether a window is on top of everything else or if the mouse is in a portion of the window that is not covered by anything else. I have workarounds I can live with for now. Aaron
