We did use this solution (appending a <script> tag into the current
page)
in the past, but it was very problematic solution. In fact, we tried
several
different approaches to implement the console/commandline.
In general, injecting anything (script or any other elements) into
every page is faulty.
According to all the experience we have - fixing the bug 591961 is the
best solution.
Or if anybody want to contribute to Firebug, issue 3358 suggests a
workaround.
Honza