It simply does what it says Rated 5 out of 5 stars

Times out password on inactivity. Should be done by firefox itself, it's essential...

Some people seem to have problem with screen timeout and lock [screen lock time doesn't count as idle time], I'd say set a shorter password timeout than lock timeout so the pw will be locked before the screen does.

Fairly impractical Rated 2 out of 5 stars

The intention is great! Really, really great. I wish Firefox would build the functionality into the browser.

Unfortunately, the timeout does not apply when waking the computer from sleep. I have a 20 minute timeout set, but if I put my computer to sleep within 20 minutes of entering the master password, it will still be unlocked when I wake the computer, say, 30 minutes later. My computer locks after an hour, but if someone cracks that, I like the added layer of FF requiring a password before autofilling website logins. And the plugin can be disabled without entering a password, so it's easy to circumvent in any case.

works great! (note that the timeout refers to *inactivity* period) Rated 5 out of 5 stars

I wonder whether the previous/first reviewer expected the master password to time out after the specified number of seconds after it was last entered. I thought that at first, too. Instead, it only times out after the user has been idle/inactive for that period of time.

In other words the purpose is not to make you always re-enter the master password every so many seconds while using the browser. Instead it only protects you for example if you walk away for so many seconds and someone starts using your browser.

BTW, this add-on is in my collection "recommended security & privacy add-ons that are minimally-invasive"

Rated 2 out of 5 stars

I had set the period as 120 seconds, but after 120 seconds nothing happened.The browser was still unlocked.
I wonder if I misunderstood the function of this addon...

More information required

If it does not seem to work, please could you give more information - what is going wrong?