I just committed a change to the definition of the .accesshide class in the core themes ('standard' on 1.9). Will go into 1.9.10 and 2.0.
.accesshide is used to indicate content which is not visible, but is still read out for screenreader users (= those who are partially sighted or, sometimes, blind).
MDL-24613 has the details, but basically, accesshide used to place content with absolute position and 'top: -100000px'. Usually this worked fine but in at least one obscure combination of html code and data in one place on our system, this managed to actually crash Safari/VoiceOver on Mac.
I have changed it to reduce the number to only -10000px (note this now fits within 16-bit integer range) and also changed it to use 'left' instead of 'top'. [And for the benefit of right-to-left languages, on those languages, it uses 'right' instead.] This should be safer and avoids potential weird scrolling issues (when creating accesshide links that become visible once tabbed to). At least it doesn't make Safari/VoiceOver crash.
If you see any problems with this, please add a comment on the bug (I don't subscribe to this forum). Thanks
--sam