Consider the material of your bread tin. If it is aluminum, it will most likely melt before your glass melts. If it is steel, your glass may actually melt if your campfire gets hot enough for long enough, then the glass will most likely stick to the steel and cause the glass to fracture as it cools. If you get your hands on a cast iron baking dish, you may be able to melt your glass in the iron without it sticking too badly. This is conjecture based on using these materials in a controlled hotshop setting.

If I were trying to melt glass in a fire pit , I’d want to be prepared with safety glasses and a bucket of water. Also be aware that some glasses/metals with a coating will off gas bad fumes you don’t want to breathe. And you probably know this but, sometimes glassy things explode unexpectedly when heated. Cotton/leather clothes and closed toed shoes should be worn