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I use twm in focus-follows-mouse mode. Mozilla-1.4-1, and before it mozilla-1.4b, frequently doesn't accept focus when the mouse enters the window. I've found no reliable way to get it to start accepting focus again -- once it gets into the state, even moving the mouse out and back in doesn't help. The only workaround is to tell twm explicitly to give focus to the mozilla window, which means that I can't type in other windows by moving the mouse, which is very annoying.
I can resolve that by opening another x11 window (xterm, mozilla or something) in the same windowmanager (twm, wmaker) space and then switching focus up and forth with moving the mouse. Little less annoying.
I seem to be able to repeat this reliably by: 1. Click in some input field in mozilla and start typing. 2. Move mouse (focus) outside mozilla. 3. Move mouse (focus) back to mozilla. Now it is no longer possible to enter anything in the field. The easiest way to fix things I've found is: 1. Click outside the input field you are trying to write in, so no field has focus. 2. Move mouse (focus) to some other window. 3. Move mouse (focus) back to mozilla. 4. Click in the input field where you want to write again. So far, both these have been reliable to trigger and solve the problem for me. Is it the same for you too?
Yes, the behavior of the bug for me is essentially as you describe.
This no longer reproduces in Fedora 0.94 beta 2
Marking CURRENTRELEASE.