How can I replace all occurences of Firefox 70's new logo?

Question

I managed to replace the icons via Resource Hacker, but there's still the new logo left when opening a new tab, which doesn't show in Resource Hacker:

Is there anyone who can tell me how to replace it?

Answer 1

On opening the Firefox executable as an archive and navigating to the ICONS folder in the resource, I could see the following icons present in it —

Of all these icons, the ones numbered 1, 2, 3, 4, 9, 10, 11 and 12 are the ones which contain the logo that you want to replace. If you replace all of them with a new icon of the same size, you should see the new tab icon changed as well.
If that doesn't work, then maybe the icon is hard-coded (though, very unlikely) in the Firefox executable that you are modifying.

However, I would always advise you to build Firefox from source to make such modifications.

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EDIT
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Apparently, my previous part of the answer was completely wrong. By changing the icons inside the main executable, it is possible to only change the Firefox branding inside the various UI elements like dialog boxes, popups and the icon visible in the app's shortcuts. However, the icons in the web pages in the app (for example the new tab page, incognito page, welcome page etc.) are located in a completely different location.

On searching the firefox source code, I found this segment which describes the location of the icons of the web pages.

So, the icons of the various web pages are not inside the Firefox executable, but in a separate location inside the installation directory.

<installation directory>\browser\omni.ja

where <installation directory> is something like C:\Program Files\Mozilla Firefox if you're using Firefox on Windows.

Inside the archive omni.ja, the chrome://branding/content/ URI corresponds to the path \chrome\browser\content\branding\. So here are the icons that you want to replace to change the icons of the various built-in web pages inside Firefox.

Reference: Searching the Mozilla source code and another similar old question on StackOverflow

How to modify the contents of the omni.ja archive?

The best way to modify the contents will be —

1. Create a folder where you have full R/W permissions (to avoid permission issues)
2. Extract the entire contents of the archive to that folder.
3. Edit/Replace the extracted files as per needs.
4. Repack the entire archive and check whether the structure matches with the original archive's structure.
5. Now, simply delete/rename the original archive from the installation directory and place the newly created archive there. (This shouldn't be difficult as long as you have an administrator-privileged user account)

For instructions on unpacking and repacking, this page might be helpful.