Will the latest versions of Firefox be brought into old Ubuntu releases?

Solution 1:

Yes, while a release of Ubuntu continues to be supported, it will receive the updated versions of Firefox.

Note that most Ubuntu releases are supported for 18 months after release. For example 10.10 is over 18 months old, and will not receive security updates, such as new versions of Firefox. There are some Ubuntu releases that are LTS (Long Term Support) releases which will continue to be supported for three or five years.

The graph below (from Wikipedia) shows the support for various releases. Yellow is the standard 18 months. Orange is the extended support on the Desktop. (Red is extended support on the Server only, this does not include Firefox.)