I'm working on JavaScript for a site, developing with Firefox, and when I refresh the page, I don't see my changes. The JavaScript file is in an external file. I reloaded and refreshed the page several times, but the old JavaScript file was still cached. Finally, I loaded the JavaScript page in the browser directly, saw the old script, hit 'reload', and saw my changes.

How can I clear cached external JavaScript files? I'll need to know this also when I tell the client that the changes are made, so that they aren't seeing the old cached functionality.