On Nightly, I see a LOT of messages like so: "Handler function threw an exception: TypeError: httpActivity.owner is null Stack: NetworkMonitor.prototype._onResponseHeader@resource://gre/modules/commonjs/toolkit/loader.js -> resource://devtools/shared/webconsole/network-monitor.js:1276:5 NetworkMonitor.prototype._dispatchActivity@resource://gre/modules/commonjs/toolkit/loader.js -> resource://devtools/shared/webconsole/network-monitor.js:900:9 NetworkMonitor.prototype.observeActivity<@resource://gre/modules/commonjs/toolkit/loader.js -> resource://devtools/shared/webconsole/network-monitor.js:962:7 exports.makeInfallible/<@resource://gre/modules/commonjs/toolkit/loader.js -> resource://devtools/shared/ThreadSafeDevToolsUtils.js:101:14 Line: 1276, column: 5" While the "errors" itself don't seem to have any real side-effects, they spam the Browser Console, making it unresponsive and far less useful, basically DoSing the Browser Console. In my case is likely to be caused by DownThemAll! setting up channels in a way the net-monitor code does not expect, but I think I saw these errors unrelated to DownThemAll! and triggered by toolkit and/or other add-on code I think. STR: - Install e.g. DownThemAll! and do some downloads - See the Browser Console (error console) fill up with messages https://dxr.mozilla.org/mozilla-central/rev/560b2c805bf7bebeb3ceebc495a81b2aa4c0c755/devtools/shared/webconsole/network-monitor.js#1254-1276 The code in question should make sure httpActivity.owner is not null (and only create that |request| objection when it isn't)
httpActivity.owner is only null because the function that was supposed to set if failed because of bug 1304752.