Ubuntu – FireFox won’t launch, “Error: Access was denied while trying to open files in your profile directory”

I cannot launch FireFox, as I'm getting the "Your Firefox profile cannot be loaded. It may be missing or inaccessible." error when I attempt to launch the latest FireFox in Ubuntu 13.04 (up to date). Bash produces the following:

(process:5052): GLib-CRITICAL **: g_slice_set_config: assertion `sys_page_size == 0' failed
Error: Access was denied while trying to open files in your profile directory.
Fontconfig warning: "/etc/fonts/conf.d/50-user.conf", line 9: reading configurations from ~/.fonts.conf is deprecated.

I do not think this is a duplicate question, as I have tried the 3 solutions that are posted in one place or another. Here they are:

(1) Remove and reinstall FF. Attempting to launch produces the same error.

(2) Rename /home/[myname]/.mozilla from bash, then create a new folder to replace it, so as to make sure that the correct user owns the directory. Attempting to launch produces the same error, both in Unity and in terminal.

(3) chown the directory from bash, with

sudo chown myname /home/myname/.mozilla

or with

sudo chown myname:myname /home/myname/.mozilla

The command executes without problems, but launching FF produces exactly the same error as before. When I check the owner of the folder, it shows the correct user (me). Recursively setting ALL permissions to 777 (so there can't be a problem with the permissions still gives the same thing.

I can run 'sudo firefox' from bash. But bash throws a warning that the profile folder has the wrong owner (i.e., it's not owned by root).

So, any ideas?

UPDATE:

Complete purge removal via

sudo apt-get purge firefox firefox-globalmenu firefox-gnome-support

and reinstall with

sudo apt-get install firefox firefox-globalmenu firefox-gnome-support

Also does not work. Exactly the same behavior as before.