When I try to connect my Trezor hardware wallet, the 'https://connect.trezor.io' popup opens but the loading circle just keeps spinning and nothing happens.
Disable 'Enhanced Tracking Protection' in Firefox. To do this:
1) Click the shield icon (next to the padlock, to the left of the URL) in the navigation bar.
2) Disable Enhanced Tracking Protection.
3) The page will reload; log in to your wallet again and pair your Trezor.