Beta and DE update twice a week at the same day (Tuesday and Thursday). When Beta reached release candidate state then it gets the same as the next release with only the update channel being Beta. During that Beta release candidate state updates for DE (aurora update channel) are halted until the first Beta for the next release.

• https://wiki.mozilla.org/Release_Management/Calendar

I think that only Nightly installs in its own installation folder and that Beta and DE need to be installed as a custom install in their own program folder, but they use their own profile folder. although you need to be cautious and best use a dedicated desktop shortcut to start each version with its own profile (there is downgrade protection, but no upgrade protection).

Is using two different shortcuts, with different profiles given in the target, still the best way to run separate instances of FF like I want (ESR & Beta or FDE)?

I've used FF ever since the days of Firebird/Phoenix 0.6--but never with multiple instances before.

Each version and/or type of Firefox (beta, Nightly . . ) should have its own profile because of compatibility issues.

Firefox Developer Edition (beta with a dark theme) definitely can coexist with the regular release without having to do anything special such as create a shortcut that targets a specific profile. Firefox 67+ takes care of that for you.

I'm not sure about beta. Also not going to experiment with it on my computer. ;-)

But actually, do you need two different versions? Since Firefox 47, there's a new internal about:profiles page where you could create a new Email profile to run with your preferred release. If you do not log that profile into your Firefox Account, you wouldn't have to worry about Sync crossing over your history, etc. And you can get a separate clump of Windows Taskbar buttons for each running profile by setting up this preference:

(1) In a new tab, type or paste about:config in the address bar and press Enter/Return. Click the button accepting the risk.

More info on about:config: Configuration Editor for Firefox. The moderators would like us to remind you that changes made through this back door aren't fully supported and aren't guaranteed to continue working in the future. Since we have had this setting for a long time and I use it myself, I feel comfortable mentioning it.

(2) In the search box in the page, type or paste taskbar.grouping.useprofile and pause while the list is filtered

Firefox should display a bar with Boolean Number String and a plus button

(3) Keep the preference type on Boolean and click the plus button to add it. If needed, double-click the preference to switch the value from false to true.

Please note when creating a new profile, Firefox will automatically make it the new default, so you'll need to click the Set as Default Profile button for your main one to avoid an unwanted surprise at your next startup.

After that, clicking the Launch profile in new browser button for your Email profile will open a new window/instance without changing your profile.

Each instance runs independently, so if you close out of your main profile, the Email profile keeps running, and vice versa.

Jscher, let me ask--would there be any benefits to doing what I want that way, compared to just having two different versions (ESR & FDE, for example) with separate profiles linked to in the shortcuts?

What is against having only the current release and not different versions like ESR or Beta or DE ?

Do you have a specific reason for using developer versions (future releases) ? If your only intention is to have a Firefox version running with a separate profile then you can simply create another profile in the current release.

See "Creating a profile":

• https://support.mozilla.org/en-US/kb/profile-manager-create-remove-switch-firefox-profiles

You can use Sync or transfer your personal data otherwise.

• https://support.mozilla.org/en-US/kb/recovering-important-data-from-an-old-profile

Jscher, let me ask--would there be any benefits to doing what I want that way, compared to just having two different versions (ESR & FDE, for example) with separate profiles linked to in the shortcuts?

The main benefit to having Firefox Developer Edition handy is that you can see what is coming down the road.

The main disadvantage with the ESR is that any bugs in that version, other than security showstoppers, are unlikely to be fixed until the next giant update. Obviously that is only a problem if those bugs affect your work.

OK if I get a bug, I can look for a fix in the next beta or release--but my experience has not been that bugs goof up my UI, but changes that are designed do. So I'd still prefer lots of time before needing to change some CSS hack.

Thanks for your input.

Jscher, let me ask--would there be any benefits to doing what I want that way, compared to just having two different versions (ESR & FDE, for example) with separate profiles linked to in the shortcuts?

The main benefit to having Firefox Developer Edition handy is that you can see what is coming down the road.

The main disadvantage with the ESR is that any bugs in that version, other than security showstoppers, are unlikely to be fixed until the next giant update. Obviously that is only a problem if those bugs affect your work. </blockquote>