Please use `data-l10n-id="fxa-accounts-header"` here, in case we have to shorten the title for some locales, and use this in the *.properties file:

```ini
fxa-accounts=Firefox Accounts
# LOCALIZATION NOTE (fxa-accounts-header): if you leave the original
# en-US value "{{fxa-accounts}}" in the following string, the localization
# will be automatically picked from the existing string with ID "fxa-accounts".
# If you need to adapt your localization to the reduced space available
# in headers, you can use a shorter string here.
fxa-accounts-header={{fxa-accounts}}
```