My thoughts. IMHO.
The problem is new plugin has "the same name" as old one i.e. it REPLACES old/original/public.
So
There should be the way to "rename" new version plugin to let them (new+old) co-exist in the system (different names, GUIDs, paths, etc); and new camera firmware should call NEW...
Hmm...
Where I mention I'm going to use this Firmware(!) on IPC-HFW1320S-W? :)
But I said that plug-in(!) from this (new) Firmware (I was ought to update plug-in in my OS/Browser after Firmware update)
doesn't support old-Firmware Dahua cameras :(
(I suppose)
So I need 2 (TWO!!) different...
After the update my IPC-HDW4431EM-ASE to "V2.800.0000005.0.R, Build Date: 2019-03-25" shows the video even in Firefox 67.0.4-64
but another Dahua camera IPC-HFW1320S-W ("2.400.0000000.16.R, Build Date: 2017-08-31") doesn't show video anymore and says "Please click here to download and install...