firefox returns odd results for file:/// or file:///tmp

Question

Not long ago (a few months at most), Firefox on Ubuntu 22.04 was able to open files in /tmp, using a file:///tmp/xxx link. Now these links show the files as unavailable.

When I try to use a file:/// link, the root dir is unrecognizable (and contains a README.md that I can't open from Firefox), and file:///tmp is also unrecognizable.

xdg-open file:/// shows the results I expect.

I've been using this for go tool cover, which no longer works because it creates a file in /tmp that the browser can't see.

Here are the contents of file:///, which might provide a clue.

README.md   1 KB     4/8/24     03:51:43 EDT
bin                  4/8/24     03:53:39 EDT
boot                 4/8/24     03:53:39 EDT
copyright   2 KB     4/8/24     03:51:43 EDT
dev                  7/4/24     13:52:01 EDT
etc                  7/4/24     13:52:06 EDT
home                 3/7/24     20:53:14 EST
host                 4/8/24     03:53:23 EDT
lib                  4/8/24     03:53:39 EDT
lib32                4/8/24     03:53:40 EDT
lib64                4/8/24     03:53:40 EDT
libx32               4/8/24     00:53:48 EDT
media                3/8/24     08:09:23 EST
meta                 4/8/24     03:53:40 EDT
mnt                  2/20/24    14:22:09 EST
opt                  4/8/24     00:53:49 EDT
proc                 7/4/24     09:48:40 EDT
root                 4/22/24    09:43:01 EDT
run                  7/4/24     13:24:58 EDT
sbin                 4/8/24     03:53:40 EDT
snap                 7/4/24     13:51:59 EDT
srv                  4/8/24     00:53:49 EDT
sys                  7/4/24     09:48:40 EDT
tmp                  7/4/24     14:15:56 EDT
usr                  4/8/24     03:53:27 EDT
var                  4/8/24     03:53:40 EDT
writable             4/8/24     03:53:23 EDT

I can't find a directory with these files anywhere on my system.

Why is this happening, and how can I fix it?

Answer 1

Ubuntu has switched Firefox from being a traditional package to being a Snap package – imagine it as a Docker container but for desktop apps. The container has a virtualized file system with its own / (and therefore its own /tmp and everything else), only with /home mounted from the outer namespace.

To 'fix' it, find a way to install Firefox not through Snap – e.g. using the Mozilla .deb packages from their PPA repository (use the apt-preferences file if needed to prioritize the PPAs over the bad Ubuntu package), or by extracting the Mozilla-provided .tar.gz into ~/.local or wherever (it will auto-update like on Windows).