Hide Tab Bar via userChrome.css Does Not Work
FF 105.0.1 64 bit, OSX 10.15.7
Could be a conflict with another addon, or perhaps my version of FF, but the instructions on hiding the native tab bar did not appear to work.
Per the post, updated about:config so legacy stylesheets would operate, and created userChrome.css in the profile folder with the suggested css code. No change. Native tab bar still there.
Also, from your description of how to find the profile folder, it sounds like you folks are on WinDoze.
On a Mac, there's no verbiage saying "Profile Directory" or "Open Directory". Instead, it's "Profile Folder", in the first big section, "Application Basics", with a "Show in Finder" URL and the actual path shown to the right. Also, after the "Important Modified Preferences" section there's "user.js Preferences", with verbiage about your profile folder and a URL to that file; examining this link also shows where your profile lives.