You should probably just use separate profiles for each Firefox instance and adapt their shortcuts. These articles may be of help:

Using a dedicated profile for Firefox Beta Switch to Firefox Extended Support Release (ESR) for personal use

https://support.mozilla.org/en-US/kb/profile-manager-create-and-remove-firefox-profiles http://kb.mozillazine.org/Shortcut_to_a_specific_profile

Your settings are not in the Firefox program folder but in a separate place. Unless you start Firefox 57 and 52 ESR with their own separate Profile, they will just start with the last Profile used.

for the time being i have uninstalled quantum and there is only the ESR version.if i follow the instructions and do the necessary changes to the installed version then installing quantum will not cause trouble?

Look, we do not have all the answers as to what code will or will not do. Experience dictates the reply. Do what you want to do. Here to put you back if need be, I will give you this information :

• https://support.mozilla.org/en-US/kb/export-firefox-bookmarks-to-backup-or-transfer
• https://support.mozilla.org/en-US/kb/profiles-where-firefox-stores-user-data
• https://support.mozilla.org/en-US/kb/back-and-restore-information-firefox-profiles

For yfi can run the Developer Edition at at the same time with compatibility mode, It is a Beta all the time and code can become unstable until nest release days/week. Gives you both worlds for now.

• https://www.mozilla.org/en-US/firefox/developer/

Please let us know if this solved your issue or if need further assistance.

i have tried to apply the instructions with the shortcut renamed to defaultuser and then chaos.i lost the profile i used.i went to the troubleshooting page under profiles and was able to recover it and then deleted what i had created before. is there any way that the installation of quantum is done in another directory than C: and if that is done is it feasible that it will not mix with ESR? using the installer it does not ask me where to install it

MmakiS said

i have tried to apply the instructions with the shortcut renamed to defaultuser and then chaos.i lost the profile i used.i went to the troubleshooting page under profiles and was able to recover it and then deleted what i had created before.

That’s odd. Typically, a default install will use the only profile available, which can be named by its default name or as modified by the user during setup and would be the only profile available unless a user added one or more. The profiles.ini file (above the /Profiles folder, such as C:\Users\<user>\AppData\Roaming\Mozilla\Firefox\) will know of that profile and have a flag indicating the profile will be used by default without asking the user. This flag is set by the "Use the selected profile without asking at startup" option in the Profile Manager dialog.

The only thing that should happen when modifying a startup shortcut (by adding -P, or -P <profile_name>) should be that Firefox asks you for the profile to choose in the first case (it opens the Profile Manager dialog), or it should use the profile defined for the last, meaning that will override the profile set as default without asking. You should not lose a profile itself just by modifying a shortcut - the step/button to remove a profile from the list and its data would be required for that. Therefor I tend to think you may have added the profile name to the shortcut, but perhaps it didn’t match the profile name, causing Firefox to not find it.

Side note: an easier way to manage profiles would be to open about:profiles, where you can create, rename or remove a profile or set one as default, but you seem to have found that. "Launching a profile in a new browser" from the available button on that page will not work (yet, unless a no-remote option is added to the shortcut, but that’s another story). Also, it’s good to back up any existing profile folders (when Firefox is closed) as well as the profiles.ini file when or before playing with profiles.

is there any way that the installation of quantum is done in another directory than C: and if that is done is it feasible that it will not mix with ESR? using the installer it does not ask me where to install it

There should be, yes. As explained in the Custom installation of Firefox on Windows article, the full installer (i.e. not the so-called "stub installer") should offer custom installation options, allowing you to define the install location. In fact, this and the profile issue also came up in a recent article discussion that you can find here and may find useful.

Bottom line is, after installing Firefox ESR, do not launch it instantly, but modify the shortcut first to either use a profile that you created beforehand using the other version, or just add -P to let you define one at that point, or it will use the default profile anyway (regardless of the Firefox install location), which is what you would like to avoid. That should be covered in the Switch to Firefox Extended Support Release (ESR) for personal use article, but if you think anything is unclear or can be added, please say so. I tend to think the shortcut info is covered for switching to ESR and creating a separate profile, but since it’s about switching to ESR (which is what most users would do), it does not cover an additional regular Firefox setup requiring its shortcut to be modified too. However it’s obvious the same would apply.

well, the point is that if someone is accustomed to engineer things he/she will find the way to do it.i'm not that kind of an expert and that is causing confusion. maybe in the future your software engineers will develop software not needing extended manipulation many thanks for your efforts to assist but i cannot and i will not use quantum under the circumstances

I’m sorry to see you feel this way. You were given steps to fulfill your wishes that took some time for others to help you out, but given the fact you marked your own final comment yourself as "solution" here as well as in your only other question, ignoring the fact that other users may find those questions too and may very well be mislead by that or even get biased because of your opinion (which is very common for forums unfortunately), I feel that you rather would remain unhappy and blame Firefox or its developers than to cooperate in a way this forum is intended for. You were also given a chance to provide feedback in a way we could improve any help articles as well as some background with regard to providing proper instructions, but to no avail.

However, you are not alone - many users feel the need to express their unhappiness related to Quantum here in some way lately, even up to insulting helpers, violating the forum rules and guidelines and ignoring the fact they may be doing something wrong, but meanwhile creating barriers for themselves. If it helps: I can run 4 or more Firefox versions and 20+ profiles and never encountered any issue, and it takes less than a minute or 2 to set things up. Firefox Quantum should and does not limit users to set up things the way they want - in fact Firefox offers more ways of customizing (including its setup) than most other browsers do. Also, profiles are used by almost any application, so they are nothing to be scared of.

To summarize: - Install both versions using the full (customizable) installer to prevent overwriting the program files by defining their install locations - Make sure to have created 2 profiles and adapt the Firefox shortcuts to contain the profile names, or just add -P to both to start with if that seems too hard

It’s not harder than that. Nevertheless, we encourage choice, so happy browsing.

I can relate my personal experience. I wanted a fresh profile for Quantum (but copying in my Places database with bookmarks and history), and to use my old profile in ESR for reference to missing add-on data or add-on functions. And to be able to run them side-by-side.

The full list of tedious steps is in this reply: https://support.mozilla.org/questions/1194097#answer-1048157