To manually install MeeTimer into Firefox:

• Remove any existing versions of MeeTimer you have.
  (In Firefox, Tools -> Addons, then find MeeTimer and click Uninstall. Now restart Firefox.)
• Download meetimer_0-21.xpi (remember where you save it!)
• In Firefox, click 'File' then 'Open File'
• Select the meetimer_0-21.xpi file you just downloaded
• Install like a normal addon

Back to http://getmeetimer.com