I have been investigating this for a little bit as part of a way to improve our chunking of browser-chrome tests (required as we have a 2 hour runtime on debug). I found that I get a timeout in browser_addons.js when running tests per directory. In fact, this test fails (timeout on foreign install), whenever it is the first test to be run in a browser-chrome session. I found that running browser/base/content/test as a set of directories works just fine, likewise running browser_addons.js after browser_blocklist.js, the summary is if browser_addons.js is run after another test, it seems to pass. The solution could be as simple as renaming the test file, but that will bite us in the future. We really need to make this work and make it work reliably. For some reason this is only affecting linux (32/64) in my tests both on try server and locally. I would be happy disabling this test until it is ready for production. Ideally we would fix it in the next week or so and move on.
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