Visual Confirmation for "Get Messages" button

[Herykos]

This isn't a critical suggestion at all but more of a user-comfort related one. I would love to have a visual aid confirming that I have pressed the "Get Messages" button to refresh my mailboxes. I know of the status bar information but I would enjoy the "Get Messages" button to visually change when clicked.
Other apps have a loading icon that appears but Thunderbird does not. 
Just nit-picking but would save me and my brain from making a few clicks

[Jon]

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