Bugzilla

I can reproduce this by calling HyperTextAccessible::TextAtOffset on the editor root, passing 0 as the offset and nsIAccessibleText::BOUNDARY_LINE_START. As to how to do this in a test, I'd probably add something to accessible/tests/mochitest/text/test_lineboundary.html.
`testTextAtOffset("your_new_id", BOUNDARY_LINE_START, ...);`

I'm a little confused by the reduced test case, as it deals with a table inside an editor, but from what I could see, the Gmail composer was an editor containing only a `<br>`. That said, I can definitely reproduce the hang with your test case, so that probably doesn't matter.

I can reproduce this by calling HyperTextAccessible::TextAtOffset on the editor root, passing 0 as the offset and nsIAccessibleText::BOUNDARY_LINE_START. As to how to do this in a test, I'd probably add something to accessible/tests/mochitest/text/test_lineboundary.html.

```
testTextAtOffset("your_new_id", BOUNDARY_LINE_START, [
  [0, 0, kEmbedChar, 0, 1],
]);
```

I'm a little confused by the reduced test case, as it deals with a table inside an editor, but from what I could see, the Gmail composer was an editor containing only a `<br>`. That said, I can definitely reproduce the hang with your test case, so that probably doesn't matter.