The "Identifier with bad escape" test fails in Firefox 3.6

The [Identifier with bad escape](https://github.com/jquery/sizzle/blob/master/test/unit/selector.js#L163) test fails in Firefox 3.6:
<img width="956" alt="Screen Shot 2019-08-20 at 00 31 21" src="https://user-images.githubusercontent.com/1758366/63304080-17d8ea80-c2e2-11e9-8e91-9a6aa2881926.png">
This is a new test, added in b2b650b629192beaf419098c459411a65121f5a1 (PR #450).