Sure, it’s a cliche. Computer not working? Restart the sucker. This time though, it paid off.
Finally decided to try disabling Firebug which required a restart of Firefox. Turns out that did the trick. Not disabling Firebug, but the restart that followed. Now with Firebug re-enabled it’s still working like a champ.
I guess the lesson is that sometimes the simplest things to try actually work.