Security features warning links to Firefox installation support page with incomplete info

Since v14.0a2, the Tor Browser has been displaying a "Security features" warning on Linux systems with unprivileged user namespaces either turned off - like older Debian systems (I saw it on stretch, but I think they are off by default on buster too) -, or turned on depending on whether a suitable apparmor profile exists for the application - i.e. Ubuntu 24.04 and higher. The warning was introduced with Firefox's bug 1899516 and points to an actual albeit obvious security issue, namely the Firefox sandbox being unable to use user namespaces in the absence of user namespaces. For Ubuntu 24.04 I think you were made aware of such issue starting from bug #42517 (closed), which links to Firefox's #1884347.

The new "Security features" warning contains a "How to fix this issue" link which brings the user to the Mozilla support page for installing Firefox on linux (first screenshot below). Only at the end of that page (second screenshot below) some information, evidently aimed at addressing the issue on Ubuntu, is provided. That info is however useless on systems with unprivileged user namespaces turned off: in this case, to have a working sandbox what you should do is turning them on using sysctl -w kernel.unprivileged_userns_clone=1 (maybe at the expense of the rest of the system). I tested that the warning disappears on stretch if you do so.

I'm not sure what Tor's policy is regarding this kind of branding, but having a link to the Firefox installation page may not be what you want to see in Tor Browser. Additionally, that kind of help is useless for systems which simply have unprivileged user namespaces turned off, as opposed to being conditional upon the existence of an apparmor profile. So I thought you might want to look into this.