A downgrade is being shown as an update...
firefox.png
pmpc.png
The left column shows the latest version.
The right column shows the version (PMPC thinks) you have.
I have had this issue when updating through the browser using the Firefox and Thundebird About screens, and reported it to Mozilla.
The About screen display is correct, but the version number in the registry is not.
Running winget also shows the version mismatch.
Mozilla couldn't reproduce it.
I now update with PMPC, and the versions are correct in both.