In Firebug, click the dropdown next to the "Console" tab, and check "Enable console for Local Files".

Many asynchronous callbacks "swallow" errors. That is, any error can occur in the callback and it won t show in Firebug or any just-in-time debugger I know of. However, with "Break on All Errors" on, Firebug will stop. Look for that in the Script tab options.

Are you using TrimPath? It can also "swallow" errors.

说实话，我不知道。但我之前遇到过Firebug的问题，重新安装约需要2分钟，通常可以解决问题。

Do you have anything like this in your javascript?

window.onerror = function(){
    return true;
};

This will suppress any normal behavior of errors.

Is the Firebug icon yellow or grey? If it is grey, then Firebug is turned off (or all the panels are disabled).