Dear Alex,
Sorry that I took so long to reply. I had just tested things too quickly, now I took a bit more time and indeed focus tracking in Firefox is not working for me (focus always goes to the upper left corner of the screen, and sinc I had only tried to type in the adress bar with the window maximized I mistakenly thought it was working). The other applications I tried are the terminal, gedit, and the file manager and they work perfectly well (I imagine it may be because they may be very tightly integrated with gnome). Thunderbird I can't say because I don't use it. So I am a little disappointed because Firefox and Emacs would be enough for me to switch from Windows to Linux but so far they don't seem to be very usable for me. If you have any suggestion, I'd be very grateful.
About displaying images in the gnome terminal, I tried to open a pdf from emacs in the terminal, and doc-view would not display it in image mode. But I'm really a beginner here so perhaps I am simply not doing things correctly.
So do you think we (or I) should submit this bug to emacs development team? I must admit I didn't understand much in this last sentence so I would probably need help to submit the bug properly and accurately.