Chrome has getManifest(), Safari doesn't have anything, Firefox has an
asynchronous API...
So, instead of using extension APIs, store the common informations
(extension name, version, homepage url) in a file (vapi-appinfo.js), which
can be included when it's needed (its data will be available at vAPI.app.____).
The file's content is updated each time the extension is being built, so
it shouldn't be modified manually.