Is there any way for Firefox to load a local Javascript file that is stored on the computer to load on startup ? Also similarly is there any way for it to be loaded if and only if the user opens a particular url pattern ? I am not talking about recognizing the exact pattern, maybe just the domain. For example all urls that have the domain of xyz.com. In the first case I want the script to be loaded for all webpages, and in the second case I want it to be loaded for only a select set of webpages. The script must be stored locally on the computer.