If Mozilla decides to upgrade to a compiler that does not have the same ABI as the current version, any built component may fail. It is a possiblity that is introduced when upgrading to a new compiler without recompiling everything. Effectively, it is a different platform.
What does this mean to you? If you build a component and it works fine in version 1.0 of Mozilla. If and when Mozilla upgrades the compiler they use, your component will have to be rebuilt against the same compiler.
When you see a
@status FROZEN, note that this means it should work as long as the component and xpcom are built with the same compiler ABI.
For more information on issues of componentization and binary compatibility, see http://mozilla.org/projects/xpcom/glue/Component_Reuse.html .