The brown stuff in the corners of your oven door (between the glass panels) is most likely a combination of food residue, grease, and dust that has accumulated over time. When you cook or bake in the oven, especially when using high temperatures or cooking greasy foods, small particles of food and oil can splatter or evaporate. Some of these particles may escape the oven cavity and find their way into the space between the glass panels on the oven door.
Over time, these particles can build up and become brown or black in color due to the combination of heat and oxidation. Unfortunately, this buildup can be challenging to clean because the glass panels are usually sealed, making it difficult to access the space between them.
Cleaning this area usually involves disassembling the oven door to access the inner glass panels and remove the accumulated residue. However, it's essential to note that disassembling the oven door can be a complex task and may void the warranty if not done correctly.
If the residue is bothering you and you feel comfortable doing so, you can check your oven's user manual or contact the manufacturer to see if they provide instructions for cleaning between the glass panels. Some oven models have removable inner glass panels, making cleaning easier. Otherwise, it's best to have a professional appliance repair technician handle the cleaning to avoid any potential damage to the oven door.
To prevent excessive buildup in the future, it's a good idea to clean up spills and splatters inside the oven as soon as they occur and to use oven-safe containers or baking sheets to catch any potential drips or spills. Regularly cleaning the interior of the oven and the door's exterior can also help prevent the buildup of stubborn residue.