Access keys are documented in section 17.11.2 of the HTML 4.01 specification. According to that documentation,
The invocation of access keys depends on the underlying system. For instance, on machines running MS Windows, one generally has to press the "alt" key in addition to the access key. On Apple systems, one generally has to press the "cmd" key in addition to the access key.
However, some evidence shows that in Firefox,
Evidently, access keys are trapped before other keys in Firefox. So when access keys are defined on a page, they mask those keys from Vimperator. This causes a problem on OS X because combinations like ^I are frequently used. It’s too bad that Firefox on OS X does not behave like Firefox on UNIX.
Major problem: On Wikipedia, the "This is a minor edit" checkbox has accesskey="i" which prevents using the ^I external editor in OS X.
In OS X, every time you hit ^I, the corresponding checkbox will toggle. Hitting ^I within the textbox should trigger the external editor, but it triggers the access key instead.
Again, on Wikipedia, the "This is a minor edit" checkbox has accesskey="i" which prevents using the ^I external editor in OS X.