A good example is the Network tab. In Chrome, I need only have the developer tools open to capture information about requests. In FF, I must not only have the tools open, but I must also be viewing the tab.
Another minor annoyance is the state of add-ons. It seems that new versions of the add-ons I use regularly are several versions behind their Chrome counterparts. And have you tried to develop an add-on? Wow. The docs are kind of harsh. They could really use a guided example.