how to reset firefox. I need to see a webpage update and its stuck in the old build.

Define "reset firefox"

if you want to wipe all settings out you can run:

mv ~/.mozilla ~/.mozilla_old

and next time you run it you will get an entirely stock profile with no favourites / skins / saved password / addons

If you do not want to lose al settings do not run that command.

Can you please clarify if I have not satisfied your question. It is a bit ambiguous.

In the case, that you only want to renew the webpage (ie https://answers.launchpad.net/):

Simply hold CTRL and press r (CTRL+r) this will cause the browser to download the webpage.