--- a/gfx/webrender/res/ps_border_corner.glsl
+++ b/gfx/webrender/res/ps_border_corner.glsl
@@ -148,16 +148,17 @@ void main(void) {
     vec2 p0, p1;
 
     // TODO(gw): We'll need to pass through multiple styles
     //           once we support style transitions per corner.
     int style;
     vec4 edge_distances;
     vec4 color0, color1;
     vec2 color_delta;
+    vec4 edge_mask;
 
     // TODO(gw): Now that all border styles are supported, the switch
     //           statement below can be tidied up quite a bit.
 
     switch (sub_part) {
         case 0: {
             p0 = corners.tl_outer;
             p1 = corners.tl_inner;
@@ -175,16 +176,17 @@ void main(void) {
             set_edge_line(border.widths.xy,
                           corners.tl_outer,
                           vec2(1.0, 1.0));
             edge_distances = vec4(p0 + adjusted_widths.xy,
                                   p0 + inv_adjusted_widths.xy);
             color_delta = vec2(1.0);
             vIsBorderRadiusLessThanBorderWidth = any(lessThan(border.radii[0].xy,
                                                               border.widths.xy)) ? 1.0 : 0.0;
+            edge_mask = vec4(1.0, 1.0, 0.0, 0.0);
             break;
         }
         case 1: {
             p0 = vec2(corners.tr_inner.x, corners.tr_outer.y);
             p1 = vec2(corners.tr_outer.x, corners.tr_inner.y);
             color0 = border.colors[1];
             color1 = border.colors[2];
             vClipCenter = corners.tr_outer + vec2(-border.radii[0].z, border.radii[0].w);
@@ -201,16 +203,17 @@ void main(void) {
                           vec2(-1.0, 1.0));
             edge_distances = vec4(p1.x - adjusted_widths.z,
                                   p0.y + adjusted_widths.y,
                                   p1.x - border.widths.z + adjusted_widths.z,
                                   p0.y + inv_adjusted_widths.y);
             color_delta = vec2(1.0, -1.0);
             vIsBorderRadiusLessThanBorderWidth = any(lessThan(border.radii[0].zw,
                                                               border.widths.zy)) ? 1.0 : 0.0;
+            edge_mask = vec4(0.0, 1.0, 1.0, 0.0);
             break;
         }
         case 2: {
             p0 = corners.br_inner;
             p1 = corners.br_outer;
             color0 = border.colors[2];
             color1 = border.colors[3];
             vClipCenter = corners.br_outer - border.radii[1].xy;
@@ -227,16 +230,17 @@ void main(void) {
                           vec2(-1.0, -1.0));
             edge_distances = vec4(p1.x - adjusted_widths.z,
                                   p1.y - adjusted_widths.w,
                                   p1.x - border.widths.z + adjusted_widths.z,
                                   p1.y - border.widths.w + adjusted_widths.w);
             color_delta = vec2(-1.0);
             vIsBorderRadiusLessThanBorderWidth = any(lessThan(border.radii[1].xy,
                                                               border.widths.zw)) ? 1.0 : 0.0;
+            edge_mask = vec4(0.0, 0.0, 1.0, 1.0);
             break;
         }
         case 3: {
             p0 = vec2(corners.bl_outer.x, corners.bl_inner.y);
             p1 = vec2(corners.bl_inner.x, corners.bl_outer.y);
             color0 = border.colors[3];
             color1 = border.colors[0];
             vClipCenter = corners.bl_outer + vec2(border.radii[1].z, -border.radii[1].w);
@@ -253,16 +257,17 @@ void main(void) {
                           vec2(1.0, -1.0));
             edge_distances = vec4(p0.x + adjusted_widths.x,
                                   p1.y - adjusted_widths.w,
                                   p0.x + inv_adjusted_widths.x,
                                   p1.y - border.widths.w + adjusted_widths.w);
             color_delta = vec2(-1.0, 1.0);
             vIsBorderRadiusLessThanBorderWidth = any(lessThan(border.radii[1].zw,
                                                               border.widths.xw)) ? 1.0 : 0.0;
+            edge_mask = vec4(1.0, 0.0, 0.0, 1.0);
             break;
         }
     }
 
     switch (style) {
         case BORDER_STYLE_DOUBLE: {
             vEdgeDistance = edge_distances;
             vAlphaSelect = 0.0;
@@ -296,17 +301,17 @@ void main(void) {
     RectWithSize segment_rect;
     segment_rect.p0 = p0;
     segment_rect.size = p1 - p0;
 
 #ifdef WR_FEATURE_TRANSFORM
     VertexInfo vi = write_transform_vertex(segment_rect,
                                            prim.local_rect,
                                            prim.local_clip_rect,
-                                           vec4(1.0),
+                                           edge_mask,
                                            prim.z,
                                            prim.scroll_node,
                                            prim.task);
 #else
     VertexInfo vi = write_vertex(segment_rect,
                                  prim.local_clip_rect,
                                  prim.z,
                                  prim.scroll_node,

--- a/gfx/webrender/res/ps_border_edge.glsl
+++ b/gfx/webrender/res/ps_border_edge.glsl
@@ -147,84 +147,90 @@ void main(void) {
 
     // TODO(gw): Now that all border styles are supported, the switch
     //           statement below can be tidied up quite a bit.
 
     float style;
     bool color_flip;
 
     RectWithSize segment_rect;
+    vec4 edge_mask;
+
     switch (sub_part) {
         case 0: {
             segment_rect.p0 = vec2(corners.tl_outer.x, corners.tl_inner.y);
             segment_rect.size = vec2(border.widths.x, corners.bl_inner.y - corners.tl_inner.y);
             vec4 adjusted_widths = get_effective_border_widths(border, int(border.style.x));
             write_edge_distance(segment_rect.p0.x, border.widths.x, adjusted_widths.x, border.style.x, 0.0, 1.0);
             style = border.style.x;
             color_flip = false;
             write_clip_params(border.style.x,
                               border.widths.x,
                               segment_rect.size.y,
                               segment_rect.p0.y,
                               segment_rect.p0.x + 0.5 * segment_rect.size.x);
+            edge_mask = vec4(1.0, 0.0, 1.0, 0.0);
             break;
         }
         case 1: {
             segment_rect.p0 = vec2(corners.tl_inner.x, corners.tl_outer.y);
             segment_rect.size = vec2(corners.tr_inner.x - corners.tl_inner.x, border.widths.y);
             vec4 adjusted_widths = get_effective_border_widths(border, int(border.style.y));
             write_edge_distance(segment_rect.p0.y, border.widths.y, adjusted_widths.y, border.style.y, 1.0, 1.0);
             style = border.style.y;
             color_flip = false;
             write_clip_params(border.style.y,
                               border.widths.y,
                               segment_rect.size.x,
                               segment_rect.p0.x,
                               segment_rect.p0.y + 0.5 * segment_rect.size.y);
+            edge_mask = vec4(0.0, 1.0, 0.0, 1.0);
             break;
         }
         case 2: {
             segment_rect.p0 = vec2(corners.tr_outer.x - border.widths.z, corners.tr_inner.y);
             segment_rect.size = vec2(border.widths.z, corners.br_inner.y - corners.tr_inner.y);
             vec4 adjusted_widths = get_effective_border_widths(border, int(border.style.z));
             write_edge_distance(segment_rect.p0.x, border.widths.z, adjusted_widths.z, border.style.z, 0.0, -1.0);
             style = border.style.z;
             color_flip = true;
             write_clip_params(border.style.z,
                               border.widths.z,
                               segment_rect.size.y,
                               segment_rect.p0.y,
                               segment_rect.p0.x + 0.5 * segment_rect.size.x);
+            edge_mask = vec4(1.0, 0.0, 1.0, 0.0);
             break;
         }
         case 3: {
             segment_rect.p0 = vec2(corners.bl_inner.x, corners.bl_outer.y - border.widths.w);
             segment_rect.size = vec2(corners.br_inner.x - corners.bl_inner.x, border.widths.w);
             vec4 adjusted_widths = get_effective_border_widths(border, int(border.style.w));
             write_edge_distance(segment_rect.p0.y, border.widths.w, adjusted_widths.w, border.style.w, 1.0, -1.0);
             style = border.style.w;
             color_flip = true;
             write_clip_params(border.style.w,
                               border.widths.w,
                               segment_rect.size.x,
                               segment_rect.p0.x,
                               segment_rect.p0.y + 0.5 * segment_rect.size.y);
+            edge_mask = vec4(0.0, 1.0, 0.0, 1.0);
             break;
         }
     }
 
     write_alpha_select(style);
     write_color0(color, style, color_flip);
     write_color1(color, style, color_flip);
 
 #ifdef WR_FEATURE_TRANSFORM
     VertexInfo vi = write_transform_vertex(segment_rect,
                                            prim.local_rect,
                                            prim.local_clip_rect,
-                                           vec4(1.0),
+                                           edge_mask,
                                            prim.z,
                                            prim.scroll_node,
                                            prim.task);
 #else
     VertexInfo vi = write_vertex(segment_rect,
                                  prim.local_clip_rect,
                                  prim.z,
                                  prim.scroll_node,