testrunner fails on firefox 50 at test qx.test.bom.element BoxSizing:testSet

[level420]

Firefox 50.0.0 (Linux 0.0.0) qx.test.bom.element BoxSizing:testSet FAILED
    supported boxSizing value was not applied!: Expected 'padding-box' but found 'content-box'!
        qx.core.AssertionError.constructor:20
        qx.core.Assert.__fail:19
        qx.core.Assert.assertEquals:28
        qx.type.BaseString.assertEquals:7
        qx.test.bom.element.BoxSizing.testSet:11
        qx.dev.unit.TestFunction:11
        qx.dev.unit.TestResult.run:23
        qx.dev.unit.TestFunction.run:7
        .runTest://localhost:9876/home/travis/build/qooxdoo/qooxdoo/framework/node_modules/karma-qooxdoo/qooxdoo-adapter.js

As per changelog for firefox 50 https://developer.mozilla.org/de/Firefox/Releases/50#Changes_for_Web_developers padding-box has been removed.

See also https://developer.mozilla.org/en-US/docs/Web/CSS/box-sizing

The bugzilla bug: https://bugzilla.mozilla.org/show_bug.cgi?id=1166728

[level420]

Fixed via #9190