Is there a policy governing use of browser extensions to enhance productivity software?
There is nothing specific to browser extensions. In practice, an extension is (merely) a small piece of code running within a (browser) environment, therefore logically it is no different from any other cloud-supplied or -hosted code running in an (OS) environment.
TL;DR; I would expect browser extensions to be treated just like any other Open Internet Tooling.
Is there a policy governing use of browser extensions to enhance productivity software?
There is nothing specific to browser extensions. In practice, an extension is (merely) a small piece of code running within a (browser) environment, therefore logically it is no different from any other cloud-supplied or -hosted code running in an (OS) environment.
TL;DR; I would expect browser extensions to be treated just like any other Open Internet Tooling.