Here is a quick way to get long lines to display more prettily on github.  Install the Stylish extension to your browser, then open up the Stylish Preferences and create a new style that looks like this:

```CSS
@-moz-document domain(github.com) {
    div.line {
        white-space: pre-wrap;
    }
}
```

It messes up the line numbers, though, so if you want to link to or comment on a particular line, you'll have to turn it off in the User Styles list.