The Ticker The badge on the toolbar button shows the time spent at the current site (the default) or the total time spent on the web today. There is an option for selecting which. This ticker shows the time in minutes. More than 59 minutes is shown as H:MM, for example 1:05 for 1 hour, 5 minutes. Click the toolbar button for a panel that shows both the time spent on the current site today and the total time spent on the web today (H:MM / H:MM). Use the panel to open the summary page or change the timing mode:

Grey mode (default): timing is automatically paused after 30 seconds of inactivity and starts up again when activity resumes (e.g. when the mouse pointer moves inside the browser window).
Green mode: keep timing despite periods of inactivity. This makes it easy to keep the timer on while watching videos.
Blue mode: only log the total time for each day and don't log which websites were visited or how much time was spent on each of them.
Timer off mode: no time or websites are logged. The button badge is not shown.

Reminder Messages Receive periodic reminder messages (after every X minutes) to help keep you aware of how much time you have spent on the web. Turn these on and set the frequency under options. The Summary Page The summary page reports how much time you have spent, and where you have spent it, for today and the past 70 days. This includes weekly summaries of the past 10 weeks and monthly summaries of the past 6 months. There is an option to change when a new day begins (for night owls who stay up past midnight). All data is stored locally on your computer. When data is more than 70 days old it is automatically deleted. Under options there is a button to delete all data. White List Under options you can enter a list of sites to prevent them from being logged, and any time spent on them from being counted. This lets you exclude work-related sites, for example. Known Issues Occasionally the idle timeout does not work correctly and too much time is logged for a given site. This appears to be a problem with Firefox's browser extensions API. See this bug: https://bugzilla.mozilla.org/show_bug.cgi?id=1383244 A workaround is to minimize or otherwise "unfocus" Firefox before leaving the computer idle. Contributions If you use and like this add-on, a small contribution or a favorable review would be greatly appreciated. Mind the Time received an honorable mention in the Amp Your Firefox Contest of 2013.