> My Firefox updates automatically, and it never told me to immediately restart the browser.

It happens all time time for me. Literally happened just a few minutes ago. It happens when you open a new tab or window, not when you're browsing within an existing tab.

> Restart to Keep Using Firefox Developer Edition

> An update to Firefox Developer Edition started in the background. You’ll need to restart to finish the update.

> Your windows and tabs will be quickly restored, but private ones will not.