As a long-term user of FF, the browser has served me well.
Of course there have been numerous pleas that Adobe Flash should be abandoned by websites due to its vulnerability. I do though have the"Shockwave Flash" plugin set to 'Ask to activate' in FF.
FF "Quantum" has the following under "Extensions":-
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When I look under FF "Add ons" for Flash, they appear to my ignorant view as being tailored for YouTube etc.
As the OP has used another browser as I suggested and not had a problem with access the issue has gone away for him. As before, for sites which don't display correctly I just load with Edge, which I don't like.
Anyway, I increasingly use browsers (including FF) within 'Sandboxie' which I suppose is overkill because both Edge and FF are supposed to have their own sandboxes. Nevertheless, 'Sandboxie' is reassuring and easy to use. Two clicks on 'clear default box' after browsing and everything is deleted.
**LINK**
(edit for line spacing)
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Edited By Fowlers Fury on 25/05/2018 12:44:46