First, install into Chrome
Click Install to get started
A confirmation question should appear at the bottom of Chrome, click 'Continue':
After that, another box will popup asking for confirmation. Approve it.
First, confirm you wish to install into Firefox
You may see a security bar at the top of Firefox, click 'Allow' to continue:
A confirmation box will appear. Click 'Install Now' to accept.
(If you don't see any of this, please click Install to start the install manually)