Table accessible tree and table interface tests for HTML tables

Mozilla Bug 410052 Mozilla Bug 417912 Mozilla Bug 493695 Mozilla Bug 512424

col1 | col2
--- | ---
col2sub1 | col2sub2
cell1 | cell2 | cell3
col1 | col2 | col3

col1 | col2 | col3
row1 | cell1 | cell2
row2 | cell3 | cell4

Test Table
| columnHeader_1 | columnHeader_2 | columnHeader_3
--- | --- | --- | ---
rowHeader_1 | row1_column1 | row1_column2 | row1_column3
rowHeader_2 | row2_column1 | row2_column2 | row2_column3

| c1 |  |  |  |

a | b