Firefox has a terrible, horrible, no good, very bad bug whereby a text input

which is disabled cannot be selected. This is especially problematic for our

install key field, which is a 40-character long hash which we want people to be

able to copy and paste.
It turns out that the "readonly" property works equally well for disabling

changes, but Firefox allows selection on those. This property is technically

HTML5 but is well-supported across all browsers.

Verified that "readonly" did the right thing in both Firefox and Chrome.