A few days back I installed Ubuntu 14.04 LTS (Trusty Tahr) on my laptop. It is a Desktop Edition.
As a default web browser it ship with Firefox version 28 . On April 29, 2014 means 4 days back, firefox released new version 29.

We can install firefox version 29 with the help of apt-get command. It is available for Ubuntu 14.04 LTS (Trusty Tahr) .

To install Firefox version 29 , run the below given command

sudo apt-get install firefox firefox-locale-en

Close the firefox web browser and open it once again.

In below given screenshot, you can see the Firefox Version 29 in Ubuntu 14.04 LTS.

You can also check the firefox version by using command

sudo dpkg -l |grep firefox

Below given is the reference from my system

sharad@linuxworld:~$ sudo dpkg -l|grep firefox
[sudo] password for sharad: 
ii  firefox                                               29.0+build1-0ubuntu0.14.04.2                        amd64        Safe and easy web browser from Mozilla
ii  firefox-locale-en                                     29.0+build1-0ubuntu0.14.04.2                        amd64        English language pack for Firefox
ii  unity-scope-firefoxbookmarks                          0.1+13.10.20130809.1-0ubuntu1                       all          Firefox bookmarks scope for Unity
ii  xul-ext-webaccounts                                   0.5-0ubuntu2                                        amd64        Ubuntu Online Accounts extension for firefox
sharad@linuxworld:~$