Can't stake ubAAMPL using Metamask + Trezor

[benavente]

After hitting "Sign" on MetaMask, I get a "Transaction failed" message and the following error in the JS console:

MetaMask - RPC Error: MetaMask Message Signature: Error: Not supported on this device 
Object { code: -32603, message: "MetaMask Message Signature: Error: Not supported on this device", data: {…} }
inpage.js:1:51499
    createErrorMiddleware moz-extension://635ae5f7-a834-4ced-b938-54aaed1edb8e/inpage.js:1
    _runReturnHandlers moz-extension://635ae5f7-a834-4ced-b938-54aaed1edb8e/inpage.js:17
    _runReturnHandlers moz-extension://635ae5f7-a834-4ced-b938-54aaed1edb8e/inpage.js:17
    _processRequest moz-extension://635ae5f7-a834-4ced-b938-54aaed1edb8e/inpage.js:17

Using Firefox, latest MetaMask extension version.