Here it is, Firefox has not offically reviewed it yet, but you can download it here, and it works.

https://addons.mozilla.org/en-US/firefox/addon/reloadevery/versions/

-Ryantiger658

No need to download anything. Just click somewhere on your web page in a blank area (that does not include links or flash or iframes) and click "Reload Every..." and choose your timer option and click on the "enable" option. Whoala!

alcrowley:

I believe that you are wrong. Firefox 5 with no extensions, does not show that option on the context (right-click) menu. To test, in Firefox 4 or 5, click Firefox button > Help > Restart with add-ons disabled; the browser will immediately close, then re-start, open a web site and see if your instructions show the "Reload every" option.