Yeah, got no idea on this one. Two “icon themes” appear to retain the correct scalable icon size: high-contrast and moka. The new desktop icon appears to be the problematic one.
Reboot, remove and re-add the shortcut from the menu, trying to “resize” the icon produces no change in the size.
Maybe a .svg issue that may have been included in all the reziable icon folders in /usr/share/app-install/icons…I otherwise have no idea.
Yeah, happening here as well now. Surely gives it an advantage over Chrome 
Ubuntu Mate 17.10, Redmond theme.
More users apparently affected on vanilla Ubuntu: https://bugzilla.mozilla.org/show_bug.cgi?id=1446262
HI all,
a fix for you:
Right click the desktop icon > Properties > Click the Mozilla icon:
then follow the path in the pic below and select the firefox.png icon. 
: (Other Locations > File system (Computer) > usr > share > icons > hicolor > 128x128 > apps).
Thank you wolfman 
It works.
It works for me too @radax05, I have marked it as solved as the OP (@daniel66666) just needs to follow my tip!. 
Hi everyone,
… not sure your fix is permanent. What does happen when you try to create a new launcher for Firefox ?
Here an other one is still big the « workaround » only applies to the actual icon on desktop.
Hi @Coeur-Noir,
it isn’t a permanent solution but it is a fix, there is obviously something wrong with the FF icon but please don’t ask me what!.
It is not a fix since it is not long-term reliable.
I did some test from a liveUSB : https://forum.ubuntu-fr.org/viewtopic.php?pid=21895919#p21895919 and upgrading FF may delete some useful folder regarding icons.
So here is a launchpad bug https://bugs.launchpad.net/ubuntu/+source/firefox/+bug/1760144 please mark yourself as affected
Confirmed here (18.04b1 patched up to tonight). This has unfortunate knock-on effects:
With the Papirus icons, there is no issue:
I think it is down to the themes but it doesn’t affect my desktop with Pocillo icons, I am sure that it will get sorted but my fix worked although not permanent!.
@wolfman
thank you, danke, gracias,спасибо,xвала,谢谢
I hope that on the next computer I will not have to learn how to adjust the CPU routine just to function properly
BUT THIS WORKS JUST FOR SINGLE ICON? 
Hi @Vladimir75,
it should be fixed anyway now?. Mine is still working fine with the full release of 18.04 
.
Are you referring to a general fix in the distribution or a workaround?
With the default theme I still have the issue on multiple installations of 18.04 .
I did a full install on 2 laptops recently and both are fine so I can only assume it has been fixed?.
I just tried it with a fresh profile on 18.04 in VirtualBox, fully updated.
Log in, drag the Firefox icon from the Brisk menu onto the desktop => huge icon.
I then tried every single theme that is installed by default, and only “High Contrast Inverse”, which uses a completely different FF icon gives you the proper size.
