<s>
GNU	B-Operating_System
LibreJS	I-Operating_System
,	O
or	O
simply	O
LibreJS	B-Operating_System
,	O
is	O
a	O
free	B-Application
software	I-Application
web	B-Protocol
browser	I-Protocol
extension	I-Protocol
for	O
Mozilla	O
Firefox-based	O
browsers	B-Application
,	O
written	O
by	O
the	B-Application
GNU	I-Application
Project	I-Application
.	O
</s>
<s>
Its	O
purpose	O
is	O
to	O
block	O
nonfree	O
nontrivial	O
JavaScript	B-Language
programs	O
and	O
allow	O
free	O
or	O
trivial	O
JS	O
in	O
a	O
user	O
's	O
web	B-Application
browser	I-Application
.	O
</s>
<s>
The	O
add-on	O
was	O
written	O
to	O
address	O
the	O
so-called	O
"	O
JavaScript	B-Language
Trap	O
"	O
first	O
described	O
by	O
Richard	O
Stallman	O
in	O
2009	O
,	O
a	O
situation	O
in	O
which	O
many	O
users	O
unknowingly	O
run	O
proprietary	B-Application
software	I-Application
in	O
their	O
web	B-Application
browsers	I-Application
.	O
</s>
<s>
GNU	B-Operating_System
LibreJS	I-Operating_System
blocks	O
nonfree	O
JavaScript	B-Language
programs	O
that	O
are	O
present	O
in	O
many	O
websites	O
.	O
</s>
<s>
It	O
is	O
developed	O
as	O
part	O
of	O
the	B-Application
GNU	I-Application
Project	I-Application
by	O
Ruben	O
Rodriguez	O
and	O
Nik	O
Nyby	O
and	O
is	O
included	O
by	O
default	O
in	O
the	O
GNU	B-Application
IceCat	I-Application
browser	B-Application
.	O
</s>
<s>
It	O
can	O
also	O
work	O
with	O
Tor	B-Application
.	O
</s>
<s>
The	O
add-on	O
allows	O
site	O
whitelisting	O
and	O
has	O
an	O
email	O
address	O
detection	O
system	O
for	O
users	O
to	O
contact	O
page	O
webmasters	O
in	O
order	O
to	O
persuade	O
them	O
into	O
making	O
their	O
JavaScript	B-Language
code	O
compliant	O
with	O
LibreJS	B-Operating_System
.	O
</s>
<s>
According	O
to	O
the	B-Operating_System
Free	I-Operating_System
Software	I-Operating_System
Foundation	I-Operating_System
,	O
many	O
websites	O
(	O
if	O
not	O
whitelisted	O
)	O
break	O
while	O
using	O
the	O
add-on	O
,	O
due	O
to	O
the	O
pervasiveness	O
of	O
proprietary	B-Application
JavaScript	B-Language
code	O
on	O
the	O
web	O
.	O
</s>
<s>
Nevertheless	O
,	O
programmer	O
and	O
activist	O
Richard	O
Stallman	O
supports	O
the	O
usage	O
of	O
GNU	B-Operating_System
LibreJS	I-Operating_System
.	O
</s>
<s>
Criticizing	O
Google	O
,	O
Stallman	O
said	O
,	O
"	O
In	O
general	O
,	O
most	O
Google	O
services	O
require	O
the	O
execution	O
of	O
non-free	O
JavaScript	B-Language
code	O
.	O
</s>
<s>
If	O
you	O
refuse	O
to	O
do	O
so	O
(	O
for	O
example	O
,	O
by	O
running	O
LibreJS	B-Operating_System
)	O
,	O
you	O
will	O
see	O
that	O
you	O
will	O
not	O
be	O
able	O
to	O
use	O
these	O
services.	O
"	O
</s>
<s>
Klint	O
Finley	O
of	O
Wired	O
,	O
after	O
going	O
without	O
JavaScript	B-Language
for	O
a	O
week	O
,	O
wrote	O
,	O
"	O
The	B-Operating_System
Free	I-Operating_System
Software	I-Operating_System
Foundation	I-Operating_System
launched	O
its	O
Free	O
JavaScript	B-Language
campaign	O
in	O
2013	O
to	O
promote	O
websites	O
using	O
only	O
free	O
and	O
open	O
source	O
JavaScript	B-Language
code	O
,	O
or	O
making	O
sites	O
function	O
without	O
it	O
.	O
</s>
<s>
To	O
help	O
users	O
avoid	O
running	O
proprietary	B-Application
JavaScript	B-Language
,	O
they	O
developed	O
LibreJS	B-Operating_System
,	O
a	O
plugin	O
for	O
the	O
Firefox	B-Application
web	I-Application
browser	I-Application
that	O
blocks	O
most	O
,	O
but	O
not	O
all	O
,	O
JavaScript	B-Language
from	O
running	O
.	O
</s>
<s>
They	O
also	O
work	O
with	O
engineers	O
to	O
help	O
reduce	O
dependence	O
on	O
proprietary	B-Application
JavaScript.	O
"	O
</s>
<s>
However	O
,	O
the	O
FSF	O
does	O
not	O
use	O
the	O
term	O
"	O
open	O
source	O
"	O
and	O
actively	O
advocates	O
against	O
using	O
it	O
,	O
preferring	O
the	O
term	O
"	O
free	B-Application
software	I-Application
"	O
instead	O
.	O
</s>
<s>
Cory	O
Doctorow	O
of	O
BoingBoing	O
,	O
discussing	O
Finley	O
's	O
article	O
,	O
said	O
he	O
had	O
used	O
NoScript	B-Operating_System
for	O
years	O
,	O
and	O
got	O
around	O
the	O
problems	O
Finley	O
identified	O
by	O
whitelisting	O
pages	O
with	O
wanted	O
functionality	O
that	O
only	O
works	O
with	O
JavaScript	B-Language
.	O
</s>
<s>
Websites	O
have	O
been	O
criticized	O
or	O
rated	O
based	O
on	O
whether	O
they	O
work	O
without	O
JavaScript	B-Language
or	O
with	O
LibreJS	B-Operating_System
enabled	O
.	O
</s>
