Rated 4 out of 5 stars

Unobtrusive. Low overhead. Gives just the right amount of information and functionality. The notification in the notification area disappears too soon. I would not like to click on it but would like to be able to set how many seconds it appears.

This review is for a previous version of the add-on (1.49). 

Hi.

Problem - Alert is being displayed for too short time.

You can adjust the duration of alert box being displayed by changing the default setting of Firefox. Four second delay for the alert being displayed is the default setting. You can change the default by typing "about:config" in the URL bar (without quotes) and pressing Enter. Then you can change the value of "alerts.totalOpenTime". The default setting is 4000 which is 4000 miliseconds, you can increase this value by yourself.
If you use Mac OS X, you can adjust the duration by changing Growl notification system option.
You should know that this will affect all add-ons that use displaying of alerts.