Thunderbird 25-30 compatibility tests

@Sancus, @mstriemer may I ask for a expedited review to get this landed before the push next week?

Thank you.
I'm not crazy about these patterns because they can match a lot of things that have nothing to do with this. It might help to wrap these numbers in `\b` so that they need to be whole words. That way `5000` won't match `15000`, etc.

```python
r"\b5000\b": 551919,
```