If you restart Firefox, does this continue occurring? If so, check out this page. Firefox requires a restart after it has updated, there is no way to get around that.

No, it's gone after restart but the point is that 1. I don't want to restart the browser 2. I don't want the reminder to be that annoying. If Firefox really can't keep working after update, developers could have forced the restart. Otherwise, why do they allow this popup to be closed (X button on the right)? If they don't want user to miss this notification, they could have shown it as a modal message box. Behaviour of this popup suggests that restart is optional. Also, it's very logical that if I closed this bar once, it means that I've acknowledged the notification and I don't need to be told about that again. From my user point of view this looks like a bug. Popup bar should not appear again after it was manually closed.

If a restart is required to upgrade and you do not restart then you do not complete the upgrade. I imagine this is offered in this way because forcing an restart may be inconvenient and in some instances could result in information loss.

To my mind that is a much better method than simply forcing a restart. You may note a restart is required when some extensions are added or disabled, again Firefox provide sa warning and does not force a restart.

Please use input if you wish to offer a short feedback comment https://input.mozilla.org/en-US/feedback#sad This is not a forum developers are likely to see.