Friday, December 7, 2012

IServiceProvider implementation in Firefox

In Firefox every MSAA accessible object implements IServiceProvider interface which is used to obtain different accessible objects that are in connection to the given one. The idea of IServiceProvider is quite close to IAccessible2/ATK relation concept but it operates on different set of relation types. It has IServiceProvider::QueryService method which is defined as:

  HRESULT QueryService(
      REFGUID guidService,
      REFIID riid,
      void **ppv

guidService identifies the accessible object you need, riid is an interface the object should be queried to.

In Firefox we support the following guid services:

IID_IAccessibleApplication  to get an IAccessible2 application accessible implementing IAccessibleApplication interface.

SID_IAccessibleContentDocument = { 0xa5d8e1f3,0x3571,0x4d8f,{0x95,0x21,0x07,0xed,0x28,0xfb,0x07,0x2e} } a Firefox specific service used to get a tab document the accessible object belongs to.

IID_IAccessibleEx used to obtain UIA IRawElementProviderSimple instance. It works under "accessibility.uia.enable" preference.

Also we support IID_ISimpleDOMNode, IID_IAccessible and IID_IAccessible2 as guid services but they are basically query interfaces and they return the same object as query interface does.

Note, all said above works in Firefox 16 and later. Prior to Firefox 16 we used to have a different logic that allowed tricks like


to get an application accessible. It's not possible anymore. Please double check your code if you rely on IServiceProvider::QueryService.

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