I am using Firefox 4.01 on GNU/Linux x86_64.
Is there any reason why there is no autoupdate? In fact, when I look at the "About Firefox" dialog, it just says "Updates available at http://www.firefox.com/".
Long story short: Install it manually (unless it comes with your Linux package management, thanks Simon Sheehan for pointing that out)
First of all,
however that applies only to security updates I suppose. That is backed up by the following statement:
This has been the process for all major Firefox version before, as they're not an important Security Update per se but a manual update you can choose to make.
So no mentioning of automatically updating the major version here as well.
The auto update is only for minor releases 4.1 4.2