Gecko_ia2 bfubBackend: ensure that ARIA treegrids get a role of table as soon as possible, so that it presents exactly like a table in brwose mode and quick nav to the table also works.
system test for ARIA treegrid: use the actual html file from the w3c ARIA practices repository, rather than a local copy, as it is very likely we will want to use more of these test cases in future.
System tests: fix get_speech_at_index_until_now so that each line (sequence) is stripped of whitespace at its beginning and end. Previously whitespace was only stripped from the ends of the entire multiline string.
ARIA treegrid system test: focus a link in the iframe before moving to the treegrid so as to not have to deal with a possible focus event on the iframe document when switching to focus mode in the treegrid later.