WebGL build runtime error

I just tried building a project for WebGL in unity 5.2, and after the unity loading screen got the error below (running it in firefox). Any ideas how to even begin figuring out what the problem might be?

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An error occured running the Unity content on this page. See your browser's JavaScript console for more info. The error was:
uncaught exception: abort(-1) at jsStackTrace@file://WebBuild/Release/WebBuild.js:1
stackTrace@file://WebBuild/Release/WebBuild.js:1
abort@file://WebBuild/Release/WebBuild.js:38
_pthread_create@file://WebBuild/Release/WebBuild.js:1
HH@file://WebBuild/Release/WebBuild.js:28
gF@file://WebBuild/Release/WebBuild.js:28
zO@file://WebBuild/Release/WebBuild.js:28
DO@file://WebBuild/Release/WebBuild.js:28
_v@file://WebBuild/Release/WebBuild.js:28
xik@file://WebBuild/Release/WebBuild.js:15
Cik@file://WebBuild/Release/WebBuild.js:15
VJg@file://WebBuild/Release/WebBuild.js:7
qJg@file://WebBuild/Release/WebBuild.js:7
nZq@file://WebBuild/Release/WebBuild.js:6
gDg@file://WebBuild/Release/WebBuild.js:11
fDg@file://WebBuild/Release/WebBuild.js:11
nDr@file://WebBuild/Release/WebBuild.js:31
invoke_vii@file://WebBuild/Release/WebBuild.js:1
NBg@file://WebBuild/Release/WebBuild.js:11
TAg@file://WebBuild/Release/WebBuild.js:11
hDr@file://WebBuild/Release/WebBuild.js:31
invoke_viiii@file://WebBuild/Release/WebBuild.js:1
SAg@file://WebBuild/Release/WebBuild.js:11
nDr@file://WebBuild/Release/WebBuild.js:31
invoke_vii@file://WebBuild/Release/WebBuild.js:1
YAg@file://WebBuild/Release/WebBuild.js:11
Uef@file://WebBuild/Release/WebBuild.js:26
Qfq@file://WebBuild/Release/WebBuild.js:6
zEr@file://WebBuild/Release/WebBuild.js:31
invoke_iiii@file://WebBuild/Release/WebBuild.js:1
HN@file://WebBuild/Release/WebBuild.js:28
Xv@file://WebBuild/Release/WebBuild.js:28
Dlb@file://WebBuild/Release/WebBuild.js:18
KIb@file://WebBuild/Release/WebBuild.js:18
jHb@file://WebBuild/Release/WebBuild.js:18
lHb@file://WebBuild/Release/WebBuild.js:18
VGb@file://WebBuild/Release/WebBuild.js:18
Chb@file://WebBuild/Release/WebBuild.js:23
SDb@file://WebBuild/Release/WebBuild.js:18
eOd@file://WebBuild/Release/WebBuild.js:14
aEr@file://WebBuild/Release/WebBuild.js:31
@file://WebBuild/Release/WebBuild.js:1
Browser_mainLoop_runner/<@file://WebBuild/Release/WebBuild.js:1
@file://WebBuild/Release/WebBuild.js:1
Browser_mainLoop_runner@file://WebBuild/Release/WebBuild.js:1

If this abort() is unexpected, build with -s ASSERTIONS=1 which can give more information.

 

I have the same error going on trying to build a test with only SocketIOforUnity - v1.0.1 in my project in 5.1.2f1