Did any of you having this issue deploy a straight DMG of any of those programs, like Firefox or Chrome "as is" from the developer without first repackaging them in Composer or another program? Because if so, the icon for the mounted disk image is usually contained at the top level of the DMG as a hidden icns file. If you push the DMG as is, it copies everything in the mounted volume to the root of the hard drive, including perhaps that hidden icon, which could end up changing the icon for the internal drive.
For example, here's what's contained in the mounted disk image for Google Chrome:
ls -al /Volumes/Google Chrome
total 568
lrwxr-xr-x@ 1 TestAdmin staff 13 Jan 16 22:37 -> /Applications
drwxr-xr-x@ 8 TestAdmin staff 272 Jan 16 22:37 .
drwxr-xr-x 5 root wheel 160 Mar 29 16:58 ..
-rw-r--r--@ 1 TestAdmin staff 8196 Jan 5 23:52 .DS_Store
-rw-r--r--@ 1 TestAdmin staff 214666 Jan 5 23:52 .VolumeIcon.icns
drwxr-xr-x@ 3 TestAdmin staff 102 Jan 16 22:37 .background
-rwxr-xr-x@ 1 TestAdmin staff 63006 Jan 5 23:49 .keystone_install
drwxr-xr-x@ 3 TestAdmin staff 102 Jan 16 00:58 Google Chrome.app
As you can see there is a hidden (prefaced with a ".") VolumeIcon.icns file, which is what gives the disk image that custom icon in the Finder. I suspect somehow that icon is being copied to the root of your hard drives and changing the icon for the drive. Again, this could happen if you don't properly repackage the app from the disk image but just try to push the disk image as is.
In fact, if you do the same ls -al command against your hard drive, like ls -al /Volumes/<name of drive here>/ you'll see a .VolumeIcon.icns file, which is actually a symlink to an icon in the /System/Volumes/Data/ path:
lrwxr-xr-x 1 root admin 36 Nov 30 12:14 .VolumeIcon.icns -> System/Volumes/Data/.VolumeIcon.icns
@goebelamy @djtaylor @jrajan @Jordan_Hare
