Mozilla has stopped supporting Firefox 4 with security updates, surprising users as it had not informed about the change following the release of Firefox 5 on Tuesday.

As part of its Tuesday's Firefox 5 release, Mozilla has patched 10 bugs in Firefox 5 and 10 of the 11 bugs in Firefox 3.6. The company said it will continue to support Firefox 3.6 for a short amount of time.

However, the company which had started shipping Firefox 4 three months ago, did not mention about fixing any bug in Firefox 4.

Following Firefox 4's vulnerability patches, Mozilla said Firefox 4 had reached EOL (end of life), Computerworld reported.

Unlike Mozilla, Google doesn't patch flaws in earlier editions of Chrome. Google's Chrome automatically gets updated in the background and is perhaps the most secured version being used by users. Google has outlined the patches it has applied in the current version of Chrome browser.

Mozilla has not conducted automatic updates so far.

However, there is a slight change in how Mozilla offers upgrades to a new version. Earlier, a pop-up window used to appear on the browser asking the user to opt for a major update offer. But now, users have to opt out. What does it mean?

A Firefox 4 user will see a pop-up window notifying the upgrade offer to Firefox 5. But, this time Update Firefox will be activated by default. However, the user can decline the upgrade either by clicking Ask Later or by closing the pop-up window itself.

Many Firefox 4 users are unlikely to opt for the upgrade as the older add-ons may not be compatible with Firefox 5.