Mozilla Firefox ESR (Extended Support Release) is a long-term support build of Firefox, updated roughly every 42 weeks for major changes and every 4 weeks for minor changes. Portable version is also available.

In other words, Mozilla Firefox ESR is designed to be three versions behind the current official release but with the latest security updates. It's for anyone who needs to use a previous build of Firefox safely. While you can download older builds manually going back to the first Firefox, they won't have the latest security updates.

Aside from the security updates included, you'll most likely not even notice that Mozilla Firefox ESR is a few builds behind.

Similar:
● How to Make Google Chrome and Mozilla Firefox Run Like New Again
● How to Remove or Edit Saved Credit Card Information in Chrome, Firefox, IE, and Edge
● How to Reset or Repair Google Chrome, Mozilla Firefox or Microsoft Edge
● How to Delete Your YouTube Watch and Search History
● How-to Mute Tabs in Google Chrome, Mozilla Firefox, and Microsoft Edge