No, these are all different.

The Extended Support Release is a version of Firefox that receives major updates only about once a year, with only security patches in the other months. This was developed for businesses demanding high stability of features for support reasons. Of course, since this currently is based on Firefox 78, it lacks some of the useful new features that have released since then.

The Developer Edition is a specially themed beta version of the next/forthcoming version (these days, Firefox 90).

There also is a Nightly version which is the next version after that (Firefox 91), but most people are not interested in daily updates, unless they have to test all of the latest browsers to plan website or add-on changes well in advance.

Thank you. So what I understand is that an ESR release combines all/select stable/security patches that were part of the multiple general firefox browser versions released since the last ESR release. Is that correct? I have a requirement where I need to ensure my web application is compatible with the next ESR release. So where can I find ESR specific beta downloads? What I see in here https://www.mozilla.org/en-US/firefox/all/#product-desktop-beta is general Firefox beta and not specific to ESR.

Please give me some pointers on this.

thanks

ESR is a designated release (last was 78, next is 91) and then instead of getting full monthly updates, it gets selected security patches.

The "new" ESR based on Firefox 91 is available for testing in parallel with the "stable" ESR based on Firefox 78. See the "Which version would you like?" selector here:

https://www.mozilla.org/en-US/firefox/all/#product-desktop-esr

Thank you. As per the Release Calendar, I can see that Release date for ESR 91.0 is 2021-08-10 Which means, can I assume it is the latest stable release or only a beta? How to identify if a particular ESR version is officially the latest stable release?

Do you mean this calendar: https://wiki.mozilla.org/Release_Management/Calendar

Current ESR users remain on the old series and are not auto-updated to the new series until after the first two releases, to provide IT departments time to test and configure. The new series isn't described as a beta.

ok.. so when exactly auto-update for 91.0 will happen? after 91.2?

Yes, according to the calendar, starting Nov. 2, 2021, all ESR users will be upgraded to 91.3.0esr.

thank you sir. that was a very very useful info. So ideally for ESR versions, the auto-update happens after 2 minor releases. meanwhile, if they want, they can always go to the download page and get it manually before auto-update. is that correct?

That is my understanding: ESR users stay on the older series until it reaches its end before getting switched to the new series. The first two releases in the new series are overlapped to allow time for testing.