Unfortunately it seems that the addon doesn't work immediately upon installtion. But there is a fix. Amazing addon after you add a quick fix! I am on a Windows machine and this is what I did. First, you need to locate the Profile Switcher config folder. This is the address:

C:\Users\Username\AppData\Roaming\nulldev\FirefoxProfileSwitcher\config

Just replace Username with your own username. If there is no file named "config.json" in there, make it. Ensure that you have this in there:

{
"browser_binary": "C:\\Program Files\\Mozilla Firefox\\firefox.exe"
}


Confirm that Windows recognizes it as a JSON source file. Restart Firefox. The addon should now work!

Works great with Firefox on Arch Linux. You do, however, have to download a helper (firefox-profile-switcher-connector-bin) from the AUR, but it's well worth it. The instructions are clearly explained after you install this plugin (in the "Complete Setup"). You also have to apply a workaround to get the connector working (something that isn't well documented):

1. Create ~/.config/firefoxprofileswitcher/config.json
2. Add to this file: {"browser_binary": "/usr/bin/firefox"}

Would be good if this extra "hidden" step (workaround) was not needed.

BTW - it's not the devs fault that this extra step is required - it's because of changes to Firefox. It's much easier using this plugin instead of opening a new tab and then entering "about:profiles" in the address bar and then selecting the profile you want to switch to.

Works nicely after applying workaround as found in the GitHub repo (Issue 106)

Insanely useful after properly setting it up.

When the add-on was working, it was ★★★★★. Now it no longer switches when I select a profile. I have to deal with it by starting with "firefox.exe -p" like in the old days.
I then switched to a derivative browser with built-in profile switching.

zero issues so far (using floorp)

Great addon.

Workarounds (including Linux) to fix the v124.0 issue: https://github.com/null-dev/firefox-profile-switcher/issues/106#issuecomment-2008582801

The solution from olivrrstray is worked!

Thanks @Shivam, your solution fixed the issue of this add-ons in MacOS :)
~~~ Terminal
> echo '{"browser_binary": "/Applications/Firefox.app/Contents/MacOS/firefox"}' >~/Library/Preferences/ax.nd.nulldev.FirefoxProfileSwitcher/config.json
~~~

Fix in MacOS: "echo '{"browser_binary": "/Applications/Firefox.app/Contents/MacOS/firefox"}' >~/Library/Preferences/ax.nd.nulldev.FirefoxProfileSwitcher/config.json"

Worked great, broke, but then followed Zein Adi/olivrrstray's instructions about creating a config.json and now working again. Thanks!

Is your extension broken? Go to this review: https://addons.mozilla.org/en-US/firefox/addon/profile-switcher/reviews/2057565/

Stopped working but followed @olivrrstray instructions below and it is working again. Thank you.

Currently down, but olivrrstray in the reviews has a fix for windows that was easy to follow, and when working properly it's fantastic, very easy to use and i love having multiple profiles available

GOOD

Took a minute to setup, but once done its an awesome experience! btw im on a Macbook Pro 2019 Intel I7

Works flawlessly on m2 pro macbook running Sonoma, honestly insane that this hasn't been implemented natively yet

Unclear and confusing in Fedora