So basically, I wanted to add the userchrome.css, but as I had none in the basic chrome folder in Zen Browser profile, I created one. as the doc said, I had to go in about:config to ENABLE devtools.debugger.remote-enabled which is originally on "FALSE". After that, I restarted the browser, and now the whole workspace feature is broken.
I tried installing the update, and coming back to the previous update, to see if it reset anything. That didn't helped. I removed some mods in case some where maybe imcompatible, doesn't work either.
So now, every time I close Zen browser, the workspace thingy disappear from my toolbar, and have to add it again manually, and then do the shortcut to switch workspace to make it appear again like it was before, which is fairly annoying. And even tho I did turned back to default the only setting I changed, it's still not working for me as it was before. When I turn off workspace in settings, it doesn't change anything, and when I turn it on, suddenly everything appears again like it was turned off. I restart the browser and again, same issue as said above. Gotta add it again to the toolbar manually and cycle through them all.
If anyone have any idea on how to fix that, please tell me, I really love Zen browser, but now that I did the workspaces this issue is really annoying.