STR:

1. Either use 2a378427bf28d7d3da0bd436516609d9b8c2caed or add ac_add_options --disable-xbl to your mozconfig
2. Run test_compute_data_with_start_struct.html

Results:

  FAIL initial and other values of border-bottom-width are different - didn't expect "2px", but got it
    SimpleTest.isnot@SimpleTest/SimpleTest.js:334:16
    round@layout/style/test/test_compute_data_with_start_struct.html:91:62
    @layout/style/test/test_compute_data_with_start_struct.html:105:6
  FAIL initial and other values of border-left-width are different - didn't expect "2px", but got it
    SimpleTest.isnot@SimpleTest/SimpleTest.js:334:16
    round@layout/style/test/test_compute_data_with_start_struct.html:91:62
    @layout/style/test/test_compute_data_with_start_struct.html:105:6
...

I'll poke.

This is a bug in the test. The test leaves the test element with -moz-appearance: radio. This is themed, so it gets the theme padding and border, rather than what the test specifies.

Now the reason it doesn't happen with XBL enabled is because the test also leaves a -moz-binding: url(foo.xml) around, which causes it to loose the frame because the XBL binding fails to load.

So removing this section from property_database.js doesn't fix the test, but exposes the test bug with XBL enabled.

(In reply to Emilio Cobos Álvarez (:emilio) from comment #2)

Now the reason it doesn't happen with XBL enabled is because the test also leaves a -moz-binding: url(foo.xml) around, which causes it to loose the frame because the XBL binding fails to load.

(And just to elaborate, since the element gets no frame with the bogus XBL binding, we hit this path rather than the other condition.

This is causing problems since leaving a non-default appearance changes margins
and borders. This was wallpapered by XBL failing to load a binding and leaving
the element without frame as described in the bug.

https://hg.mozilla.org/mozilla-central/rev/119ad04b0efc