Comment 10 for bug 1278942

Francesco, thanks for the update. I have the same output here.

Lee, I don't think quotes in /etc/environment make a difference either, but better use 'export' in the terminal, else the variable won't reach child processes:

$ export GTK_MODULES=gail:atk-bridge
$ firefox

This isn't necessary when you do it in one line, I think:
$ GTK_MODULES=gail:atk-bridge firefox

Then run this again to check if the module is loaded, good output would be like Francesco's above:
$ grep -i atk-bridge /proc/$(pidof firefox)/maps

If there is nothing, check if this file exists:
$ stat /usr/lib/x86_64-linux-gnu/gtk-2.0/modules/libatk-bridge.so

and try this
$ firefox --gtk-module=/usr/lib/x86_64-linux-gnu/gtk-2.0/modules/libatk-bridge.so

If that fails there should be message like
Gtk-Message: Failed to load module "/usr/lib/x86_64-linux-gnu/gtk-2.0/modules/libatk-bridge.so"

Check again if the module is loaded:
$ grep -i atk-bridge /proc/$(pidof firefox)/maps