Installing more than one extension
From MozillaZine Knowledge Base
You can occasionally encounter problems with Firefox when installing more than one extension at once. When you install the second extension you may be asked questions relating to the installation of the first extension.
While this problem is intermittent, its effects are not yet well known. To avoid this problem restart the browser after installing each extension.
This problem will be addressed in a future release (before 1.0).
