Ubuntu guys have changed it. Try to download firefox directly from mozilla page.

ok that's surprising, but i suppose nothing to be done about it.

If you use Firefox from the Ubuntu repositories then you can only update Firefox via Ubuntu software management just like with other applications installed this way. Ubuntu also modifies its version and may add extension.

Only the official builds of Firefox (for Linux) from Mozilla (say www.mozilla.org/firefox/all/) get internal updates.

Third-party builds like those provided Firefox packages from Linux distros do not get internal Firefox updates from Mozilla but through your distro package software management as said. Also if you build Firefox yourself you will not get updates from Mozilla as they did not well build it.

If you do use a Firefox tarbal from Mozilla make sure the Firefox folder has read/write permissions for the user so you can get updates. An easy option is to put the Firefox folder in Home if an only user.