eb2eef529f
There is no guarantee that a tab has finished loading when the test resumes. As a result, it is possible for the page action's visibility state to reset (to invisible) between calling `pageAction.show()` and `pageAction.isShown()`. To prevent that from happening, wait until the tab has finished loading before resuming the test. Differential Revision: https://phabricator.services.mozilla.com/D61125
