Hello. The top 1.5" of my Firefox browser window randomly disappears. "Disappears" = turns white (despite background or other colors) and becomes non-actionable (screen shot attached). Possible connection: it most often happens during or after using the horrible Blackboard program (web-based version) for my online classes. However, I have seen it happen when Blackboard was not currently in use, and once it happened after a reboot when Blackboard had not been used at all that session. If I have multiple browser windows open (which is rare--I use tabs), they are all affected at the same time. If I close Firefox and open it in a new window, the problem exists on the new window too. When it happens, the only recourse is to reboot my computer entirely. Aside from changing the auto-download location, I have not customized Firefox and have not installed any plugins. (Some may have been installed automatically such as those for Microsoft Office.) HELP?????