Mozilla revealed Firefox 4 will feature an auto-update similar to Google Chrome, most of the updates to the browser will be downloaded in the background and be installed automatically without prompting for user confirmation;
"We'll only be using the major update dialog box for changes like [version] 4 to 4.5 or 5," Faaborg said in a late July message on the "mozilla.dev.apps.firefox" forum. "Unfortunately users will still see the updating progress bar on load, but this is an implementation issue as opposed to a [user interface] one; ideally the update could be applied in the background."
The final decision is still up to the user, you can decide whether you want to accept the auto-updates, or stay with the current setup. This is unlike Google Chrome that gives you no option for the auto updates. Chrome is the big player when it comes to auto-updates, it kicked off in September 2008, and still relies on the then controversial update method.