We don't have a Comcast account, so I am not sure we could login to Xfinity. Meanwhile, you can try below solutions and see if it helps. 1)Try disabling your installed extensions :- Click the menu button (3 horizontal lines on top right ) and choose Add-ons. In the Add-ons Manager tab, select the Extensions panel. Click the name of an extension in the list to select it. Click Disable to disable the selected extension. Repeat this for each of the other extensions in the list. Click restart Firefox 2)Also try the steps provided in below link. Adobe Flash protected mode in Firefox | Firefox Help
... View more