When running geolocation tests repeatedly, using: ./mach mochitest-plain dom/tests/mochitest/geolocation --repeat N the tests start to time out after a few iterations. Typically a low N such as 1 or 2 is enough to reproduce the issue. After some digging, it seems that the tests time out because the test server network_geolocation.sjs simply stops getting requests from the network provider, even though it is still up and running, since I can access it using curl. After the timeout, several of the XHRs attempted by the network provider result in error (that is, have their onerror callback called). I wonder if we're hitting some sort of limit to how many XHRs can be done by a single page? I've found that throttling the number of requests the network provider does while testing alleviates the problem and gets more iterations of the tests to run: replacing 200 with 5000 or so at https://mxr.mozilla.org/mozilla-central/source/dom/system/NetworkGeolocationProvider.js#101 , for instance, causes one request to be fired every 5 seconds instead of 200ms. Filing this bug in case someone else comes across this issue. I can investigate this further if it turns out to be a bigger problem.
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