Top toolbar left margin being set to -465 px in Firefox only

For some reason this happens only in firefox, but the top toolbar is being set to -465 px, so that most of it is offscreen. Specifically the BRToolbar element, here is the computed css:

div#BRtoolbar {
    position: relative;
    left: -465px;
    right: 0;
}

Just wondering, what could cause this to be calculated that way?
