Any chance we could try (load) your page on our machines?
Note that we are concentrating on fixing bugs in Firebug 2,
can you try it and let us know if this version is fixed?
Firebug 2 announcement is here:
https://blog.getfirebug.com/2014/03/26/firebug-2-0-alpha-1/
And you can install from:
https://getfirebug.com/releases/firebug/2.0/firebug-2.0a1.xpi
I know this is a BAD report. As the application I'm writing is properly working and FireFox is displaying the page properly, this is merely an annoyance in FireBug's display and maybe others already noticed this behaviour and it might be normal? I couldn't find something similar yet.