Even though i3 cannot know the width/height of some workspaces as
long as they are not initialized (say you used workspace 1 and 3,
but not workspace 2), some applications require this information.
In this case, it was Firefox which intersects the available workareas
(see mozilla/gfx/src/gtk/nsScreenGtk.cpp) and did not position some
windows correctly when being confronted with zero-width/height
workspaces.
Please note that rdesktop’s -g workarea option will not work on
64-bit systems at the moment because of a bug in rdesktop (see the
rdesktop-devel mailing list).
Michael Stapelberg