The purpose of this API is basically to satisfy AMO reviewers in the
future, since the use of innerHTML with variables (i.e., not plain text) will
be rejected without any questions.
Since this is not a problem for browsers other than Firefox, they will
use simple innerHTML assignment, however safe-parsing could be implemented
for them too.
Since there is no API for localization in Safari, we read the locale files
every time when an extension page opens.
This commit adds a new file "make-locale-safari.py", which will make the
size of the locale files smaller.
