This kind of concatenation won't work. It should be something along the line of
```
# LOCALIZATION NOTE(fxa-notice): {{tos-link}} and {{privacy-link}} will be 
# replaced with active links. Strings with id "fxa-tos" and "fxa-privacy"
# will be used as text for these links.
fxa-notice = By proceeding, I agree to the {{tos-link}} and {{privacy-link}}  of Firefox cloud services.
fxa-tos = Terms of Service
fxa-privacy = Privacy Notice
```
And then work out the replacement in JavaScript.