Visual difference between disabled and active btn-secondary is very low
I've just been working with a lot of "secondary" buttons and have noticed that there's actually very little contrast between the active and disabled variants. It's not as noticeable when done side-by-side, but I've found myself having to mouse over buttons to confirm they're disabled rather then visually checking.
Firefox on linux (centos7) seems to be better due to thicker default font choice in comparison to chrome.
Not sure what could be done to increase the contrast. Making the disabled font even lighter would help, but that would probably decrease readability. Alternatively perhaps making the inner-border of the active btn-secondary thicker would improve the contrast