Sorry, I don't understand how these two help pages for sync solve my issue - can you elaborate? As I stated, I've read lots of help pages, forum threads, and articles about the sync and profiles features but none seem to offer the information I need.

Sync works both ways and there is no master device (i.e. all devices are equal). So if you would connect your home computer to a Sync account you use on your work computer then you download data from your work computer to your home computer, but you also upload your personal data from the profile you use on the home computer to the Sync server which merges this to your work computer and that is likely not what you want. With Firefox Sync you can only us a separate profile on your home computer and connect that to your work computer's Sync account to be able to access this data at home and make your home computer behave the same as you work computer. As soon as you do personal things with this profile on your home computer then you will find this on your work computer as well. Note that you can have multiple Firefox instances open at the same time each with its own profile, but best is probably to install a different theme on each so you can see which you are using.

Thanks for your response cor-el, this clears up a few things for me, I appreciate it. So if I understand correctly, it's impossible to keep work and personal stuff separate on multiple devices with firefox? That is, it's impossible to have separate work/personal profiles that can be accessed over two devices and will sync when changes are made? I'm unsure how your final point about multiple browser instances fits in here - does it mean I can achieve what I'm trying to or not?

The only way to keep things separate is by using a separate profile, one to connect to the work account and possibly another account for home although there no real need if you only have one home device (Sync is aimed at syncing data between multiple devices).

Do you want to have access to home things on your work computer ?

Mainly wanting access to work stuff on home device. Also should clarify, I'm wanting changes to bookmarks/passwords/addons etc to be reflected in each profile regardless of which device I'm using it on. So do you mean a profile can connect to multiple sync accounts?

No. you need to connect a profile to one Sync account only, so you need to use a second profile to connect this to another device like the work computer.

Yes I've already had it set up like this for a while:

Personal account with profile Work account with profile

And I've been using each account/profile combination on the corresponding device. So how do I switch between them then? If I go to sign in with my work account on my personal laptop I get a message pop up which says

"Are you sure you want to sign in to sync? A different user was previously signed in to sync on this computer. Signing in will merge this browsers bookmarks, passwords, and other settings with [work account email]."

I want it to remain separae. So...what do I do?

There are two possible scenarios:

(1) Configure Sync to ONLY share the data you want shared between home and work. See: How do I choose what information to sync on Firefox?

(2) Configure two separate profiles (data folders on disk) on your home system, one isolated and one sync'd, for greater privacy.

To implement #2:

(A) In your existing home profile, do NOT connect to a Firefox Account, or connect only to a Firefox Account based on a personal address that is not the one you use on your work system.

(B) Create a new profile on your home system to connect to the same Sync account as your work system. Launch a new window this profile when you want to deal with work stuff from home. To set that up:

Profile Setup

Inside Firefox, type or paste about:profiles in the address bar and press Enter/Return to load it. You probably will want to bookmark this page.

Take a quick glance at the page and make a mental note of which Profile has this notation: This is the profile in use and it cannot be deleted. That is your current default profile.

Create the profile

Click the "Create a New Profile" button, then click Next. Assign a name like WORK, ignore the option to relocate the profile folder, and click the Finish button.

Firefox will switch your default profile to the new one, so click the Set as Default Profile button for your regular one to avoid an unwanted surprise at your next startup.

Launch the profile and first time configuration

Scroll down to WORK and click its Launch profile in new browser button.

Firefox should open a new window that looks like a brand new, uncustomized installation. (Your existing Firefox window(s) should not be affected.) In this window, you can sign in to the Firefox account you share with your work system.

It doesn't matter whether you close your default profile window(s) or your WORK profile window(s) first, they are independent.

Wow, so this is very helpful jscher2000 thank you, but it also suggests profiles and sync were never specifically designed to do what I'm trying to achieve. Out of curiosity, is there an official page detailing this anywhere?

The first scenario doesn't allow me to keep work and home separate while still being able to access work stuff from home (and keeping everything up to date if changes are made) so I guess thats out.

The second scenario uses the isolated profile as the home one and a sync'd account as the work one, right?

So in this scenario, every time I wanted to access my work stuff I'd have to launch a new window through the work profile and then sign in to the work sync account?

Maybe I should let go of keeping everything separate and just use the one account on work and home devices. Not ideal, but much simpler. Anyway, thanks all for your help.

Profiles are ancient and mostly hidden, while Sync was developed years later as an add-on called Weave before eventually being built into the browser. Any profile can use Sync as a service, but Sync is not designed to separate things, only to combine them. Better integrating them would be a good goal, but considering all the use cases, I'm not sure how much simpler it actually could be.

An easier goal would be to provide direct access to profiles on the toolbar, similar to how Chrome handles "persons" (Chrome's version of profiles). Similar to Firefox, Chrome offers the ability to optionally sign into the same or a different Google Account for each person, or no account. A better UI would make it clearer how parallel these features actually are, even if they are inadequate in a similar way.