I have tried disabling both Console, Script and Net panels and then it feels much faster.
After trying to re-enable them one-by-one what I have found is that the Net panel does not make any difference, but both Console and Script panels make Firebug slow down a lot: both when enabled together and also separately.
Same here, Ubuntu 12.04, Firebug 1.10.6, Firefox 16.0.2.
Opening a tab where Firebug is active takes about one second which is far too slow, opening the debug window at the bottom of the screen is just the same.
Paddelboot