Comment 1 for bug 498574

As suggested on irc and in the pastebin, the first rule removed was probably doing more that resetting.

-#maincontent {
- clear: both;
- float: left;
- width: 100%;
- margin-right: -25%;
- }

I translated this rule to

.yui-t4 .yui-main {
    clear: both;
    float: left;
    }

to fix the issue.