When you are absolutely sure your line is correct save the file and exit the editor.
We must now empty the content of your .mozilla/firefox/xxxxxx.default directory. To do this we have to shut down Firefox completely to avoid Firefox from re-create the profile. You can copy the relevant part of the guide to a text file or use another browser for the next part, but you have to exit Firefox before erasing the content. Before you empty the folder, doublecheck that you have a copy of the content of .mozilla/firefox/xxxxxx.default in the directory .mozilla/firefox/profile and I recommend an extra copy somewhere safe.
When Firefox is closed erase the content of .mozilla/firefox/xxxxxx.default. Look down to the left corner in the Nautilus window and remember the amount of free space you have in your .mozilla/firefox/xxxxxx.default directory.
When this is done locate the file tmpfs_firefox.sh we created earlier and doubleclick it. A window will appear. Chose Run in terminal.
You will now see a terminal window open and close very quickly. This is normal and due to the fact that the whole process went very quickly. The script mounted your Firefox profile into your computer's RAM. Double-click again on the file tmpfs_firefox.sh and select once more Run in terminal. The same thing happens as before but with the difference that the script synchronized the contents of the folder with your profile folder xxxxxx.default.
Now enter the folder xxxxxx.default. You should now see that the erased files are back.