new layout is too wide

This is probably not what you want but it's still a possibility. It should be possible to zoom out in your browser. In firefox it is ctrl num+/num-

here's a firefox-specific style i added with stylish. it gets rid of horizontal scrollbars for me, reduces the vertical space between giveaways, and hides giveaways you've already entered. the sidebar from the giveaways list is reflowed horizontally over the giveaways instead of vertically next to them. if anybody has tips for making the "Browse" and "My Giveaways" headings behave themselves instead of drifting up i'd appreciate them:

@namespace url(http://www.w3.org/1999/xhtml);

@-moz-document domain("steamgifts.com") {
  body {
    min-width: 900px;
  }
  .nav__button {
    padding: 0 1em;
  }
}
@-moz-document url("http://www.steamgifts.com/"), url-prefix("http://www.steamgifts.com/giveaways/search") {
  .widget-container {
    display: block;
  }
  .sidebar, .sidebar__navigation {
    display: flex;
  }
  .sidebar {
    padding-bottom: 1em;
  }
  .sidebar__search-container {
    margin-bottom: 0;
  }
  .sidebar__heading {
    margin-left: 1em;
    border-bottom: none;
    margin-bottom: 0;
  }
  .sidebar__navigation {
    padding-bottom: 0;
  }
  .widget-container > div:not(:first-child) {
    border-left: none;
    box-shadow: none;
    margin-left: 0;
    padding-left: 0;
  }
  .giveaway__row-outer-wrap {
    padding: 0;
  }
  .giveaway__row-inner-wrap {
    padding: .5em 0;
  }
  .is-faded {
    display: none;
  }
}

+1. I also feel that the rightmost and leftmost elements (avatar and site logo, but other parts too) are too close to the window's edge.