Pre-execute external javascript for every page in firefox

Is there any method that I can pre-execute some javascripts for every page in firefox? I have tried the greasemonkey extension, but the script is e开发者_运维技巧xecuted after page loaded. I would like the "pre-executed" solutions. Can anyone help me? Thanks in advance.

that is an old post but I think you should consider using 'on load' body property. If you call your video object on load, the page would have been completely load and ready to execute your object that have been loaded before.

Already solve that kind of synchronization Pb before with this little option.