If all you want to do is execute your own js on a certain web page, you can just use greasemonkey or another userscript extension for your browser instead of writing a whole new extension each for each script.
Greasemonkey also appears to provide an interface for peristent local storage as well. [1]
The lay user is probably more likely to install a chrome extension than code. Then again, I don't know if greasemonkey has gotten more lay-friendly recently.
Greasemonkey also appears to provide an interface for peristent local storage as well. [1]
[1] http://wiki.greasespot.net/GM_setValue