Why doesn't Firefox from Canonical get updated?

[Lukas Erlacher]

Hi Chris,

According to your signature you are running a long-term support release 
of Ubuntu, which by design skews against frequent updates because of the 
idea that updates very frequently introduce new bugs or even just 
unwanted changes in functionality. This means updates are typically 
limited to critical security patches backported onto a version of the 
package that was locked in when the Ubuntu distribution was released, 
with all other patches ignored.

Ubuntu, at least in LTS versions, tries to perform the service of 
keeping your software stable and running without any change noticeable 
to you and the tasks you perform.

Please also note that because package maintenance is largely a volunteer 
effort, there may be delays in updates for anything but the most 
critical security issues.

I hope this explanation helps you understand the Ubuntu LTS Update 
process better!

Like explained by Francis, you can get "hotter" packages from 
third-party repos or PPAs if someone has decided to maintain one 
(sometimes the upstream authors of software decide to run repos 
themselves, which may be considered if not stable, at least trustworthy. 
Of course, including arbitrary software sources into your Ubuntu 
installation means you have to make sure they are trustworthy and stable 
yourself.)

(Disclaimer: I am in no way connected to the people at Canonical / 
Ubuntu that design, implement and enforce update policies. I'm just a 
user. See below for references that state the official Ubuntu policies.)

Best,
Luke

References:
https://wiki.ubuntu.com/LTS
https://wiki.ubuntu.com/StableReleaseUpdates