Bug 1089867 uncovered that we had to close and reopen the manager window in the testPreferencesButton in browser_gmpProvider.js. The minimum for testPreferencesButton to pass is to close and reopen the manager window the first four times that the inner for loop is executed, i.e. the four times that we set the enabled pref to false (twice for OpenH264, twice for Adobe EME). Anything less than that will make us fail with either 1 or 2 failures. Closing and reopening the manager window seems wrong because: * we lose a little bit of test-coverage and * we may have uncovered an underlying issue here We should figure out if we're dealing with some stale AddonManger UI state here, and fix accordingly.