The firefox update can be downloaded as *.tar.gz from the official website.
We can directly move to the downloaded directory and untar it . It will give us a folder named firefox .Inside that , we will be having an executable named firefox. Once you trigger the executable , the new version of firefox will launch.
But, we have a problem here. The existing version still exists in home folder as .firefox . And if you take an attempt by clicking on the firefox icon, it will launch the older version of your firefox.
We need to find out the directory where the firefox is installed. In my case, it was in /usr/lib . Sometimes, it may get installed in /opt or /etc. we need to replace the /usr/lib/firefox directory with our downloaded latest firefox.
sudo cp -r /home/user/download/firefox .
Enter the password to proceed with the action.
After the copy, when you click on the firefox icon , new version of the firefox will open.