Comment 5 for bug 173554

FYI, this problem appears to be caused by a permissions issue in your home directory. For instance, if you start Firefox by using "sudo firefox", some files in your Firefox profile directory will become owned by "root:root". To fix, run the following:

sudo chown -R $(id -u):$(id -g) ~/.mozilla/firefox/

Alternately, to avoid this problem in the future, be sure to use "sudo -H firefox" to set the root user's home directory before starting Firefox (disclaimer: you should avoid running Firefox as root).