Because ice-ssb is abandoned on Linux, I searched for alternatives and I found it! This extension works and it feels much better and modern then ice-ssb ever was.
Installation was maybe more complicated then any other add-on, but it was very well guided, so the whole process went without problem.
A very nice suprise is the access to Firefox extensions, settings, about:confing and others from the titlebar. I have never saw a titlebar in Plasma KDE with menus and additional elements! This rocks!

Works great, no more trouble trying command line shenanigans

Thank you. This extension allows me to keep using Firefox due to the unfortunate fact that Firefox does not support SSB anymore. You are awesome!!!!!!

Doesn't work on on MacOS Monterey, at least for me. Ran the terminal script, waited for that to finish, tried installing the additional software, which failed for some reason. Don't know how to undo the terminal script.

Works pretty good; however, in Mac OS, I usually use Alfred and/or Spotlight search to navigate through the system.

Generally what I would expect is that if an app is already running, I can use spotlight or Alfred to take me to that running instance right away. That way I can rapidly navigate through the UI. However, with this extension, when I look for the name of my installed app and hit enter, if there's an instance running already, it doesn't care and creates a second instance, which completely breaks my navigation. Small thing, but it would be cool if it could be patched (other apps in system don't create another instance unless we explicitly tell them so, so it would be nice if this could be the case for this SSB solution as well)

Firefox, please hire this developer

This is my Number 1 missing feature from Firefox, and it works seamlessly with all my web apps that I use for libraries, communication, organization, etc. Thanks!

That add-on is amazing, i really like it, but, the sessions synced log off on installed apps, for example, my icloud session is on in firefox tab, but in the pwa is logged out.

and the firefox sync service is apart for the runtime

Impressive piece of software from an attentive dev who clearly knows their stuff — darn near doing Mozilla's job for them. Was expecting a total bust first trying it out, but _it just worked_, allowing me to avoid keeping chrome around just for the magic PWA button.

In fact, this extension does an even better job than chrome's native PWA support in many regards. It seamlessly integrates the Firefox theme/layout engine with my native windowing system in a way that makes standalone PWAs appear indistinguishable from full blown desktop apps. Seriously awesome stuff.

Setup was bit of a hassle as despite the setup page saying otherwise, it never installed 7zip for me.
So i was stuck there for a moment.
Then the addon didn't appear around the other add-ons, so i couldn't make pwa's on every page I wanted.
But later it just appeared next to ublock origin in the user interface.
From there it did make it possible for me to create pwa's from every page I wanted, so while installation was bit complicated hassle it does everything that it promises to.
So 5/5 addon in my book.