Your best to lookover at Firefox sync FAQ.

https://support.mozilla.org/en-US/products/firefox/backup-recovery-and-sync/sync-data

https://support.mozilla.org/en-US/kb/sync

"how does sync work" https://support.mozilla.org/en-US/questions/1209391

Mark: Thanks for your input. I thought I had already investigated all those threads, but I revisited them as part of my “due-diligence”. Your first thread led me to https://support.mozilla.org/en-US/kb/switching-devices which I had seen before but went through more thoroughly this time. The pertinent clue, which I missed the first time, was the lack of a “Switching to a new device” button/option when I opened the FF Help Menu. I think I now know what my problem is: I’m just too old!

Specifically, my “Primary” Profile (that I want to clone) is on an older iMac, which can only be upgraded far enough to support Firefox 78.15.0esr, which apparently does not provide the “Switching to a new device” option. So that avenue is not available to me. FF78 does support a Sync function, but as I have not actually enabled that yet (anxiety), it remains to be seen whether I will encounter any “compatibility” issues.

I have however successfully “restored” my FF78 Bookmarks to a Windows10 machine running FF132, so at least that seems to work. So then it’s just a matter of transferring the 143 Logins I have in my FF78 Profile.

So there is obviously a good solution for anyone able to run a sufficiently current version of Firefox that supports the “Switching to a new device” option. Unfortunately, that doesn’t include me.

So my original question necessarily becomes: Is the “blank Profile B” concept an effective “work-around” for transferring a Profile from an older version of Firefox that doesn’t support the “Switching to a new device” option?

Any further insight/experience with this specific situation would be appreciated. I suspect that I will ultimately just have to cross my fingers and try it out, in which case I will try to report back for the benefit of my fellow Luddites obliged to run older versions of Firefox.

If you want to really clone then doing sync doesn't catch everything.

Then you should look here.

https://support.mozilla.org/en-US/kb/restore-bookmarks-from-backup-or-move-them https://support.mozilla.org/en-US/kb/back-and-restore-information-firefox-profiles https://support.mozilla.org/en-US/kb/switching-devices

"How do I save my Firefox profile data" https://support.mozilla.org/en-US/questions/1381158

https://support.mozilla.org/en-US/kb/how-restore-browsing-session-backup

"How do I backup a session (all the open tabs) so that it can be reloaded after a computer factory reset?:" https://support.mozilla.org/en-US/questions/1257866

I use google to find all these links. So use search as well those are most likely asked and posted links already.

Mark: Thanks again for your input. You’re exactly right: if I want to clone my Profile, I should just … clone my Profile! That is, just copy my entire “Profile A” folder from Device A and “install” it as the new “Profile B” on Device B. The link https://support.mozilla.org/en-US/kb/back-and-restore-information-firefox-profiles that you referenced (notably the section headed “Restore to a different location”) describes the procedure in sufficient detail that even I was able to follow it. I did a couple of experiments and was successfully able to transfer my “Primary” Profile from Firefox 78.15.0esr on my old iMac to FF 115.17.0esr on a slightly-newer Mac-Mini, and even to FF132 on Windows10. The good news is that all 143 of my Logins transferred! I really only care about my Bookmarks and Logins, but transferring the entirety of my Profile still seems the most straight-forward way to accomplish this.

A couple of caveats I will note for the benefit of anyone else who might stumble across this post later:

1) It is not strictly necessary to create a NEW Profile on Device B, considering that everything of interest has already been gleaned and that there is nothing left in Profile B that needs to be saved. The entire Profile can be overwritten per the described procedure. Otherwise, a new Profile can be created from the “about:profiles” page before closing Firefox.

2) It IS necessary to actually overwrite the target Profile B. I initially thought I could just copy my Profile A folder over, stick it in the Profiles folder on Device B, and then “switch” to it. But Firefox apparently doesn’t “see” any profiles that it did not itself create, hence you must either create a NEW Profile to overwrite, or overwrite the existing one.

I’m going to start again from scratch with a “fresh” Profile A and transfer it to my Devices B and C before initiating Firefox Sync. Wish me luck.

Final (?) Note

I completed the transfer(s) just fine. It’s actually a pretty straight-forward way to “clone” a Profile to another device. My problem came when I tried to Sync all my Profiles together. The FF115esr and FF132 Profiles Sync together just fine, but nothing was getting through to FF78esr. Then I discovered that Sync was disabled for FF 78 ([https://support.mozilla.org/en-US/que.../1440543] ) … annoying to say the least. The curious part is that in FF78 the Toolbars, Menus, Preferences, etc., even my Firefox/Mozilla Account, all look and act like Sync is enabled and functioning … but it’s not. I guess I’ll just have to use one computer to access the Internet, and another to actually get stuff done ;-)

I am nevertheless compelled to summarize my experience for the benefit of anyone else wanting to do this.

Recap: Transferring/Cloning a Firefox Profile from one device to another

This effectively “harmonizes” information in disparate Profiles (presuming you have not already enabled Sync), and could be extended to more than one device.

Scenario:

Device “A” (Profile A): Your “Primary” Device/Profile. This is already setup mostly/exactly the way you want it with most/all of the information you want to retain and transfer.

Device “B” (Profile B): Your “Secondary” Device/Profile. If this is an existing device, it may or may not have unique information that you want to preserve. If starting with a fresh install on a new device, then the default Profile is essentially superfluous.

Procedure:

1) Back-up everything first (of course!).

[https://support.mozilla.org/en-US/kb/back-and-restore-information-firefox...]

2) Glean any unique information to be preserved (Bookmarks, Logins, etc.) from Profile B and incorporate it into Profile A. Groom Profile A to get it exactly how you want it.

3) Make a backup copy of the “harmonized” Profile A (per above link). This will be used as the “template” to be transferred to your Secondary Device(s).

4) Copy the Profile A “template” folder to the target Device B (via flashdrive, NAS, or …).

5) On Device B, create a NEW Profile B (“about:profiles”), or if there is nothing worth saving you can just re-use the existing Profile B.

6) Locate the Device B Firefox Profiles folder (as described in above link, or can also be located via “about:Support” page) and open it in a Finder/Explorer window.

7) Quit/Exit Firefox.

8) Open the Profile A “template” folder and the local Profile B folder in side-by-side windows. Delete (!) everything in the Profile B folder. Move everything in the Profile A template folder to the Profile B folder.

9) Open Firefox. If necessary, select the newly-cloned Profile as the default Profile (“about:profiles”) and restart. Firefox on Device B should now magically appear exactly the same as on Device A!

10) Now you may Login to your Mozilla account and enable Sync, if you so desire.

I hope this might be of help to someone. It may be a little intimidating, but it’s pretty straight-forward if you’re careful and take it a step at a time.