working with older extension technologies

[joncat]

I've been looking at creating a new add-on to support visual testing.
I'd like to build something that sits alongside Selenium-IDE.
Looking at their code it seems I need to learn the add-in layout/standards/build-technologies before WebExtensions and Add-on SDK (though closeish to this).

The older styles seem to have same basic content as Add-on SDK, but different file structures, manifest files, development environments. There is a lot of help on the web, but it covers such as range of technologies its confusing and time-consuming. Is there a page to provide a timeline etc.

helloworld: http://kb.mozillazine.org/Getting_started_with_extension_development
preflight: http://adam.goucher.ca/?p=1331

Any general advice on integrating?

[joncat]

I have seen the Extending Selenium section in http://release.openqa.org/selenium-core/1.0/reference.html
and have tried to access the Selenium object (eg Selenium.prototype.doTypeRepeated = function(locator, text)...) in a Add-on SDK extension - but get 'not found'

What is correct way to access