User Agent: Mozilla/5.0 (Windows NT 6.3; WOW64; rv:42.0) Gecko/20100101 Firefox/42.0 Build ID: 20151029151421 Steps to reproduce: I simply upgraded Firefox 32-bit to version 42. Then I went to https://www.youtube.com/ and started watching a video. Actual results: I saw a black line on the video (see the two screenshots attached). It appears on all the youtube videos only when the controls are visible. Expected results: I should see videos without a black line like with firefox 41.

looks like Bug 1211264

I dupe this bug has the other has provided some details about his graphics.

(forget my previous comment) Gráficos Asynchronous Pan/Zoom ninguna Descripción del adaptador ATI Radeon HD 4600 Series (Microsoft Corporation - WDDM v1.1) Direct2D habilitado true DirectWrite habilitado true (6.3.9600.17999) Drivers del adaptador aticfx64 aticfx64 aticfx32 aticfx32 atiumd64 atidxx64 atiumdag atidxx32 atiumdva atiumd6a atitmm64 Fecha del driver 6-20-2012 GPU #2 Activa false ID de dispositivo 0x9490 ID de fabricante 0x1002 ID de subsistema 20091787 Procesador WebGL Google Inc. -- ANGLE (ATI Radeon HD 4600 Series (Microsoft Corporation - WDDM v1.1) Direct3D11 vs_4_1 ps_4_1) RAM del adaptador 1024 Soporta decodificación H264 por Hardware true Ventanas con aceleración gráfica 1/1 Direct3D 11 (OMTC) Versión del driver 8.97.10.6 windowLayerManagerRemote true AzureCanvasBackend direct2d 1.1 AzureContentBackend direct2d 1.1 AzureFallbackCanvasBackend cairo AzureSkiaAccelerated 0

(sorry duplication, @Julien, @Loic)