With the amount of information provided, I would like to ask your assistance to confirm that is not something caused by something amiss in your profile (possible installed addons?). So, in order to check this, can you please install the same firefox version but in a different disk drive location (starting this version will cause the creation of a new profile, without affecting your existing one). Start up that newly installed version, login to Washington Post and please report if the problem is reproducible. If the problem doesn't reproduces on the clean profile (from the different location firefox), that means most likely one of your addons is the culprit, so disable one by one your addons and retest the issue.
Bug 1700918 Comment 1 Edit History
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With the amount of information provided, I would like to ask your assistance to confirm that is not something caused by something amiss in your profile (possible installed addons?). So, in order to check this, can you please install the same firefox version but in a different disk drive location (starting this version will cause the creation of a new profile, without affecting your existing one). Start up that newly installed version, login to Washington Post and please report if the problem is reproducible. If the problem doesn't reproduces on the clean profile (from the different location firefox), that means most likely one of your addons is the culprit, so disable your addons one by one and retest the issue.