Bugzilla

Currently, it's difficult to diagnose what went wrong when there are policy problems. 

__Expectations:__
The `about:policies#errors` section should at least mention which policy (by name) wasn't applied or the type of problem encountered.

__Implementation notes:__
Administrators are more likely to be able to fully interpret detailed error messages, so we don't have to go into too much detail, but narrowing the search would help a lot.

Currently, it's difficult to diagnose what went wrong when there are policy problems. 

__STR:__

```json
{
  "policies": {
    "Preferences": {
      "browser.policies.test.nonexistent": { "Status": "locked" }
    }
  }
}
```

**Result:** one row, containing the literal string `Error running`.

**Expectation:** the row names the policy and the reason, so the administrator can tell which of their policies failed.