Created attachment 474064 [details] Test harness to demonstrate the issue When displaying a canvas that has been transferred to an offscreen canvas, the offscreen canvas may go blank, especially when switching to other windows, but even while the Safari window appears in the background. This can be reproduced with the attached offsceen_safari_blanking.html test harness. When viewing this page, after putting the Safari page in the background and doing other tasks on my Mac, the offscreen canvases will go blank. The normal "on screen" canvases will continue to show their content. Only after clicking "redraw" to cause the canvases to be updated, will they reappear. It seems that one workaround it to use the bitmaprenderer context in an on screen canvas to retain the image. However, this is less desirable as it may introduce additional latency or jank in the display of the newly drawn frame depending on the business of the main thread, and may have additional performance implications for memory use and buffer copies.