This is how you can ask compass what the usage threshold cutoff for each browser version is.

compass_browser_support_thresholds.scss

@each $browser in browsers() {
  .#{$browser} {
    @each $version in browser-versions($browser) {
      threshold: $version omitted-usage($browser, $version);
    }
  }
}

output.css

.android {
  threshold: "2.1" 0;
  threshold: "2.2" 0.02085;
  threshold: "2.3" 0.07647;
  threshold: "3" 1.11224;
  threshold: "4" 1.11224;
  threshold: "4.1" 1.96726;
  threshold: "4.2-4.3" 3.98318;
  threshold: "4.4" 6.02691;
  threshold: "4.4.3" 6.97231;
}

.android-chrome {
  threshold: "36" 0;
}

.android-firefox {
  threshold: "31" 0;
}

.blackberry {
  threshold: "7" 0;
  threshold: "10" 0.11032;
}

.chrome {
  threshold: "4" 0;
  threshold: "5" 0.02146;
  threshold: "6" 0.03577;
  threshold: "7" 0.05722;
  threshold: "8" 0.07153;
  threshold: "9" 0.08584;
  threshold: "10" 0.10014;
  threshold: "11" 0.12875;
  threshold: "12" 0.2432;
  threshold: "13" 0.28612;
  threshold: "14" 0.32188;
  threshold: "15" 0.3505;
  threshold: "16" 0.38626;
  threshold: "17" 0.41487;
  threshold: "18" 0.43633;
  threshold: "19" 0.49356;
  threshold: "20" 0.50786;
  threshold: "21" 0.53647;
  threshold: "22" 0.92989;
  threshold: "23" 1.05149;
  threshold: "24" 1.10156;
  threshold: "25" 1.15163;
  threshold: "26" 1.20886;
  threshold: "27" 1.4306;
  threshold: "28" 1.96708;
  threshold: "29" 2.09583;
  threshold: "30" 2.39625;
  threshold: "31" 2.58939;
  threshold: "32" 3.18309;
  threshold: "33" 3.65518;
  threshold: "34" 4.49924;
  threshold: "35" 5.83685;
  threshold: "36" 34.22715;
  threshold: "37" 34.3416;
  threshold: "38" 34.49181;
  threshold: "39" 34.49181;
}

.firefox {
  threshold: "2" 0;
  threshold: "3" 0.00715;
  threshold: "3.5" 0.08584;
  threshold: "3.6" 0.1073;
  threshold: "4" 0.25036;
  threshold: "5" 0.28612;
  threshold: "6" 0.30758;
  threshold: "7" 0.34334;
  threshold: "8" 0.3648;
  threshold: "9" 0.41487;
  threshold: "10" 0.44349;
  threshold: "11" 0.50786;
  threshold: "12" 0.56509;
  threshold: "13" 0.69384;
  threshold: "14" 0.74391;
  threshold: "15" 0.79398;
  threshold: "16" 0.85836;
  threshold: "17" 0.9585;
  threshold: "18" 1.03718;
  threshold: "19" 1.08726;
  threshold: "20" 1.14448;
  threshold: "21" 1.21601;
  threshold: "22" 1.48067;
  threshold: "23" 1.57366;
  threshold: "24" 1.65234;
  threshold: "25" 1.85263;
  threshold: "26" 1.94562;
  threshold: "27" 2.11729;
  threshold: "28" 2.30327;
  threshold: "29" 2.61085;
  threshold: "30" 9.14869;
  threshold: "31" 13.8339;
  threshold: "32" 14.02703;
  threshold: "33" 14.04133;
  threshold: "34" 14.04849;
}

.ie {
  threshold: "5.5" 0;
  threshold: "6" 0.0093;
  threshold: "7" 0.28815;
  threshold: "8" 0.42381;
  threshold: "9" 4.88544;
  threshold: "10" 7.48554;
  threshold: "11" 10.11579;
}

.ie-mobile {
  threshold: "10" 0;
}

.ios-safari {
  threshold: "3.2" 0;
  threshold: "4.0-4.1" 0;
  threshold: "4.2-4.3" 0.00667;
  threshold: "5.0-5.1" 0.04668;
  threshold: "6.0-6.1" 0.2334;
  threshold: "7.0-7.1" 0.96695;
  threshold: "8" 6.66198;
}

.opera {
  threshold: "9.5-9.6" 0;
  threshold: "10.0-10.1" 0.00715;
  threshold: "10.5" 0.02146;
  threshold: "10.6" 0.02985;
  threshold: "11" 0.03715;
  threshold: "11.1" 0.05214;
  threshold: "11.5" 0.06036;
  threshold: "11.6" 0.06766;
  threshold: "12" 0.08196;
  threshold: "12.1" 0.10342;
  threshold: "15" 0.42531;
  threshold: "16" 0.43246;
  threshold: "17" 0.43961;
  threshold: "18" 0.44677;
  threshold: "19" 0.46823;
  threshold: "20" 0.48253;
  threshold: "21" 0.54691;
  threshold: "22" 0.6542;
  threshold: "23" 1.01901;
  threshold: "24" 1.02616;
}

.opera-mini {
  threshold: "5.0-7.0" 0;
}

.opera-mobile {
  threshold: "10" 0;
  threshold: "11.5" 0;
  threshold: "12" 0;
  threshold: "12.1" 0.01987;
  threshold: "22" 0.07948;
}

.safari {
  threshold: "3.1" 0;
  threshold: "3.2" 0;
  threshold: "4" 0.00869;
  threshold: "5" 0.11599;
  threshold: "5.1" 0.30912;
  threshold: "6" 0.9815;
  threshold: "6.1" 1.31054;
  threshold: "7" 1.88278;
  threshold: "8" 3.52082;
}