I have ubuntu firefox; version 39.0.3+build2 that was installed a few minutes ago.

After changing security settings yesterday: I asked firefox to delete cookies at the end of each session; I found next time I attempted to load firefox that it gave only the outlines of the firefox screen: ie a homogenous grey over the screen with the closing buttons top-right; and nil else; the linux "force quit" function allowed me to close it; I ran it from a terminal; was offered a refresh function; and that restored it; I shut the computer down; I turned it on today; firstly installing the new firefox function; clicking the firefox icon gives the same frozen screen; rebooting and running from the terminal gives the same unfinished effect;