I use Thunderbird on MacOS, and after a recent upgrade, the icon in my dock changed to the default piece of paper with the Application “A” symbol on it. This made it surprisingly difficult for me to find the icon when I needed it. It’s amazing how ingrained things become or maybe I just don’t like change. Needless to say, I needed to find a way to get it back.
To fix this, I first closed Thunderbird. Then, I right-clicked on the Thunderbird icon in my dock and choose “Options” and then “Show in Finder”. You can also just open the Applications directory through Finder as well. I found Thunderbird in the Applications list. I then right-clicked on it and choose “Get Info”.
This opens a new window of the options and settings for Thunderbird. At the very bottom right-corner, there is a tiny lock symbol. You need to click on this to unlock the settings so you can change them. You may have to enter your password to unlock this.
Once it was unlocked, I saw that the normal Thunderbird icon was in the Preview section, but at the very top of the window where the app title and date last modified are listed, I could see that default app icon instead.
I clicked and held on the correct Thunderbird icon in the Preview window and then dragged it up and dropped it on the incorrect icon at the top. This replaced the incorrect icon with the correct one. I then clicked the lock in the bottom right corner to re-lock the settings before closing them.
The incorrect icon was still showing in the dock, so I removed Thunderbird from the dock by right-clicking on the icon and choosing “Remove from Dock”. I then grabbed the Thunderbird app in the Applications directory and dragged it onto the dock to readd it. The icon was now the correct Thunderbird icon, and all was right again in Dock world.