Google Chrome or Chromium is required, but it appears you don't have it installed.
Google Chrome or Chromium version or newer is required, but it appears you have an older version.
The add-on is currently in the process of being reviewed and signed by Mozilla, until then it can be installed the following way:
about:debugging
page, "Load temporary extension"Either from the about:debugging
page like above, or:
about:config
page set xpinstall.signatures.required
to false
Wallets for other browsers will be provided in the near future.