Stove glass is often held in with clips and if this is the case then a lubricant such as WD-40 applied to the bolts will help to loosen then as it is not uncommon for them to rust up. 

The glass should not touch the metal of the stove door and should be buffered by seals in order to allow for any expansion to occur safely. Seal come in one of two forms, there will either be a rope that comes in various diameters (6, 8 or 10mm) in this case the rope is bound to the stove door by rope adhesive (which is heat proofed).

Alternatively glass will be held in with a laddered rope or gasket, these both perform the same function and are interchangeable. The gasket is being fazed out and therefore it is more common for a rope seal tape to be supplied. This is 2mm thick by 15mm wide and is self adhesive one side (therefore glue is not required) and will wrap around the glass to cushion it during any expansion.

Expansion of the glass onto bare metal will lead to strain and cracking. 

When refitting the glass, ensure not to over tighten any clips or fittings as this can restrict expansion of the glass, leading to cracking. Clips should therefore only be finger tight to allow for any expansion in the glass.