This obviously breaks in a sandboxed environment. Example: 15:17:38 INFO - Sandbox: SandboxBroker: denied op=0 rflags=101101 perms=3 path=/tmp/bug293834-serialized.html for pid=4609 error="No such file or directory" 15:17:38 INFO - [Child 4609] WARNING: NS_ENSURE_SUCCESS(rv, rv) failed with result 0x80520015: file /builds/slave/try-lx-d-000000000000000000000/build/src/embedding/components/webbrowserpersist/nsWebBrowserPersist.cpp, line 2304 15:17:38 INFO - TEST-INFO | started process screentopng 15:17:41 INFO - TEST-INFO | screentopng: exit 0 15:17:41 INFO - 1332 INFO SimpleTest START 15:17:41 INFO - 1333 INFO TEST-PASS | embedding/test/test_bug293834.html | Modified textarea a-textbox form state not preserved! 15:17:41 INFO - 1334 INFO TEST-PASS | embedding/test/test_bug293834.html | Modified textarea a-prefilled-textbox form state not preserved! 15:17:41 INFO - 1335 INFO TEST-PASS | embedding/test/test_bug293834.html | Modified textbox a-text form state not preserved! 15:17:41 INFO - 1336 INFO TEST-PASS | embedding/test/test_bug293834.html | Modified textbox a-prefilled-text form state not preserved! 15:17:41 INFO - 1337 INFO TEST-PASS | embedding/test/test_bug293834.html | Modified checkbox checked state not preserved! 15:17:41 INFO - 1338 INFO TEST-PASS | embedding/test/test_bug293834.html | Modified radio checked state not preserved! 15:17:41 INFO - 1339 INFO TEST-PASS | embedding/test/test_bug293834.html | Modified select selected index not preserved 15:17:41 INFO - 1340 INFO TEST-UNEXPECTED-FAIL | embedding/test/test_bug293834.html | uncaught exception - NS_ERROR_FILE_NOT_FOUND: Component returned failure code: 0x80520012 (NS_ERROR_FILE_NOT_FOUND) [nsIFileInputStream.init] at doApply@chrome://specialpowers/content/specialpowersAPI.js:146:10 15:17:41 INFO - apply@chrome://specialpowers/content/specialpowersAPI.js:211:30 15:17:41 INFO - getFileContents@http://mochi.test:8888/tests/embedding/test/test_bug293834.html:73:5 15:17:41 INFO - persistDocument@http://mochi.test:8888/tests/embedding/test/test_bug293834.html:115:12 15:17:41 INFO - @http://mochi.test:8888/tests/embedding/test/test_bug293834.html:124:28 15:17:41 INFO - SimpleTest._newCallStack/rval@http://mochi.test:8888/tests/SimpleTest/SimpleTest.js:146:17 15:17:41 INFO - EventHandlerNonNull*this.addLoadEvent@http://mochi.test:8888/tests/SimpleTest/SimpleTest.js:171:13 15:17:41 INFO - @http://mochi.test:8888/tests/SimpleTest/SimpleTest.js:1371:5 15:17:41 INFO - simpletestOnerror@SimpleTest/SimpleTest.js:1582:11 15:17:41 INFO - OnErrorEventHandlerNonNull*@SimpleTest/SimpleTest.js:1562:1 15:17:41 INFO - JavaScript error: chrome://specialpowers/content/specialpowersAPI.js, line 146: NS_ERROR_FILE_NOT_FOUND: Component returned failure code: 0x80520012 (NS_ERROR_FILE_NOT_FOUND) [nsIFileInputStream.init] 15:17:41 INFO - MEMORY STAT vsizeMaxContiguous not supported in this build configuration.

browser/base/content/test/general/browser_printpreview.js I'm also seeing a bunch of [task 2016-09-19T17:06:59.917221Z] 17:06:59 INFO - Sandbox: SandboxBroker: denied op=0 rflags=2204000 perms=0 path=/usr/share/zoneinfo/ for pid=1296 error="Invalid argument" in the test logs, i.e. an open() of a directory, which we do not allow.

Crash reporter/leaktest: [task 2016-09-19T17:08:32.233327Z] 17:08:32 INFO - Et tu, Brute? [task 2016-09-19T17:08:32.240279Z] 17:08:32 INFO - XPCOM_MEM_BLOAT_LOG: /tmp/tmpSsQbWM.mozrunner/runtests_leaks.log [task 2016-09-19T17:08:32.240591Z] 17:08:32 INFO - Writing to log: /tmp/tmpSsQbWM.mozrunner/runtests_leaks_tab_pid1296.log [task 2016-09-19T17:08:32.241847Z] 17:08:32 INFO - Sandbox: SandboxBroker: denied op=0 rflags=2101 perms=3 path=/tmp/tmpSsQbWM.mozrunner/runtests_leaks_tab_pid1296.log for pid=1296 error="No such file or directory" [task 2016-09-19T17:08:32.243580Z] 17:08:32 INFO - Sandbox: SandboxBroker: denied op=0 rflags=1101 perms=3 path=/tmp/GeckoChildCrash1296.extra for pid=1296 error="No such file or directory"

browser/base/content/test/general/browser_printpreview.js [task 2016-09-19T17:28:40.320378Z] 17:28:40 INFO - Sandbox: SandboxBroker: denied op=0 rflags=302 perms=3 path=/tmp/1XK8NY.tmp for pid=1812 error="No such file or directory" [task 2016-09-19T17:28:40.322732Z] 17:28:40 INFO - [Child 1812] WARNING: NS_ENSURE_SUCCESS(rv, rv) failed with result 0x80004005: file /home/worker/workspace/build/src/layout/printing/nsPrintEngine.cpp, line 671 traced this down to: http://searchfox.org/mozilla-central/rev/dbbbafc979a8362a1c8e3e99dbea188fc832b1c5/widget/gtk/nsDeviceContextSpecG.cpp#130

Mass wontfix for bugs affecting firefox 52.