About a week ago I published the Firefox 22 Add-on Compatibility post. Today I learned about a new compatibility-breaking change that could affect some add-ons, though it seems to be unlikely. I would have mentioned it in my previous post if I had known about it then, so I thought it was necessary to post this update.
nsIFilePicker crash if overriding component has not implemented a domfiles getter. This crash bug was recently filed, caused by an add-on that overrides the nsIFilePicker component. The crash appeared in Firefox 22, due to bug 832923, which changed the nsIFilePicker interface. So, if your add-on does that, you should update its implementation to make sure it includes the domfile and domfiles getters.
The crash bug will be fixed so that Firefox doesn’t crash even when faced with the interface mismatch. However, affected add-ons still won’t work correctly unless updated.