What do you see when you open the More troubleshooting information page? The refresh button is shown in the image attached.

The "corrupt" message typically indicates a mismatch between the certificate used to "sign" the extension and the signing certificate built into Firefox. That should only affect very old extensions or old versions of Firefox. Another possibility is that a web server or security filter is sending an error page, which isn't a valid extension file.

Are you installing the current release from the following page:

https://addons.mozilla.org/firefox/addon/norton-password-manager/

If "Add to Firefox" doesn't work, what happens when you right-click that button and "Save Link As..."? What should appear is a Windows Save As dialog with the file name "norton_password_manager-8.2.4.982.xpi". (The full link is https://addons.mozilla.org/firefox/downloads/file/4559975/norton_password_manager-8.2.4.982.xpi.)

When you check the drop-down list from the Downloads toolbar button, the file should be about 14.5MB. Does that seem normal so far?

Regarding the Refresh button, when the feature was first introduced, this button would be missing from profiles that were not set as the default profile on the about:profiles page. However, there might be other reasons that are harder to chase down.

https://drive.google.com/file/d/1Xc4TJomqETKUOMIa9y1IgVD_alu_dIlg/view?usp=drive_link

I didn't realise the link didn't work, hopefully this one does