The Extended Support Release (ESR) has been introduced by Mozilla when the organization switched from its previous release system to the rapid release process. ESR has been designed for businesses, organizations and enterprises that deploy the web browser on their computer systems. This version of the browser aims to reduce the cost it takes to test new versions of the browser before deployment.
What this means is that some features will become available at a later time to ESR users than to users who have installed a regular version of Firefox on their system.
While ESR versions of Firefox and Thunderbird are made available mainly for organizations and enterprises, home users can also download and install ESR versions on their computer systems.
The version number scheme of Firefox and Thunderbird ESR releases indicated updates during the cycle with an increase of the digit after the second point, e.g. Firefox 17.0.4.
The first digit refers to the version of Firefox the ESR version is based on, the digit after the second point to the number of release cycles that passed since that. In this case, the ESR is based on Firefox 17 and has gone through four release cycles so far. You can simply add the digit after the second point to the first digit to come up with the current stable version of the browser.
Mozilla announced plans to change the release scheme slightly in regards to ESR versions of the browser. The idea is to move the digit after the second point to the first point. Firefox 17.0.4 would become 17.4 instead.
Why? Because Mozilla believes it is easier to "associate an ESR version with its mainline equivalent in security patches". The change, currently tracking for a Firefox 23 release would then become active for the first time when Firefox 24 is released. Firefox 24 marks the beginning of the update period of Firefox ESR from 17.0.7 or 17.0.8 to Firefox 24.0 or 24.1..
Mozilla notes that this can impact add-on developers as they need to make sure to adjust the max version information of their add-ons to take this into account. So, instead of using 24.0..* they need to use 24.*. instead for compatibility purposes.Advertisement
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