On the plus side, the only tab rename extension I've found that actually uses capture groups in regex properly. On the downside, regex doesn't seem to work in URLs, only on page titles. And I mean regex doesn't work on URLs at all, not just with capture groups - only match I can get on any URL is (.+) (i.e. "there is a URL"). Nothing else matches any actual URL as far as I can tell.

Would definitely give 5 stars if regex (with capture groups) worked on URLs.