Thank you for responding! That looks like it might work, though I side-stepped the issue by rebuilding the image from scratch (took the whole month :( ). But if we see this again, we'll try your...

I am using this thread because it perfectly shows the process of making Chrome or FF the default browser, and then a back-up process in case there's trouble with that, and how both are failing.
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Windows 1709, making minor updates to the corporate image (that we have had no trouble with over the last few updates this year). For the first time, we are seeing the same issue as the...