diff -up firefox-78.0/gfx/skia/skia/src/gpu/GrColor.h.mozilla.bmo1005535 firefox-78.0/gfx/skia/skia/src/gpu/GrColor.h
--- firefox-78.0/gfx/skia/skia/src/gpu/GrColor.h.mozilla.bmo1005535	2020-06-25 16:16:34.459083304 +0200
+++ firefox-78.0/gfx/skia/skia/src/gpu/GrColor.h	2020-06-25 16:17:00.968174743 +0200
@@ -64,7 +64,7 @@ static inline GrColor GrColorPackRGBA(un
  *  Since premultiplied means that alpha >= color, we construct a color with
  *  each component==255 and alpha == 0 to be "illegal"
  */
-#define GrColor_ILLEGAL     (~(0xFF << GrColor_SHIFT_A))
+#define GrColor_ILLEGAL     ((uint32_t)(~(0xFF << GrColor_SHIFT_A)))
 
 /** Normalizes and coverts an uint8_t to a float. [0, 255] -> [0.0, 1.0] */
 static inline float GrNormalizeByteToFloat(uint8_t value) {