There is the full download and the update 'stub.'

<strike>Note: many FAKE notices go out claiming something needs updating.

. Whenever you get a message / popup that software / files need to be updated;

DO NOT USE ANY OF THE PROVIDED LINKS

While this may be a legitimate message, it could also be Malware or a Virus. Any time you want or need to check for upgrades, go to the website of the True Owner of the program in question. For example, to check out Firefox, go to https://www.mozilla.org {web link}

You can report such a site at; Google Report Phishing Page {web link} which is the same when done while on site by going to Help > Report Web Forgery

Help us safeguard Mozilla’s trademarks by reporting misuse {web link}</strike>

Hi, it's a long running practise that partial update files are generated that minimise the download size for users updating from a fairly recent version. You can find those partials at https://ftp.mozilla.org/pub/firefox/releases/48.0.1/update/

ulric said

On Tuesday, 23 August 2016, I was alerted by Firefox, version 48.0, that an update was available. Using an administrative Windows (version 8.1 Pro) account, I authorized Firefox to update to version 48.0.1. I observed that the Firefox updater downloaded exactly a file size of exactly 11.9 MB. I wanted to confirm the size of the download, so I visited https://ftp.mozilla.org/pub/firefox/releases/48.0.1/win64/en-US/. The size of the downloadable image is 45 MB. I thought that Firefox ALWAYS installs its browser as though there were no existing instance on the target machine (i.e removing the old version, and installing the new one). In the past, when I have observed the installer perform a version update (not sure if it was a major on minor update), it seemed to download a full version. Is the Firefox version 48.0 to 48.0.1 upgrade performed by its internal updater performed by downloading a small file containing a modular component (11.9 MB in size)? Thank you.

The 11.9 MB in size is correct for the en-US firefox-48.0-48.0.1.partial.mar update. If you miss a update the patch can be a larger partial to even full patch that is not compressed like the full setups on Windows are.

See https://ftp.mozilla.org/pub/firefox/releases/48.0.1/update/win64/en-US/

What you found was the full Win64 Firefox setup for Windows.

The desktop Firefox is not just for Windows but also for Mac OSX and Linux so updates are done in a more cross platform way vs using say .exe

FredMcD, please read the question again, especially last part. Also for Windows Firefox (only) the stub is not for updates but a online installer while full setup is complete offine installer.

Hello,

Thank you for quickly answering my question. I will now mark this thread as solved.