Re: My Java plugin in Firefox does not work.
In my experience when I used to install the Java version, I removed the Ice tea plugin using Yast. That'll definitely save you from rewriting things. Also since you want the Java version, while you're in Yast remove the OpenJDK that comes with Opensuse by default. Earlier versions of Libre office needed the OpenJDK. I'm not real sure but It seems to me the last time I used the Java version of java (in 12.1) The LO that came with it could use & I think I enabled it to use then Java version 6 update 33 IIRC.
Since 12.2 came out & with all the problems coming out about Java under Oracle I personally now just use the OpenJDK & iced tea.
For that reason I'm not that sure about Java's relationship to LO these days, though I'm very sure about the browser plugin parts.
One more thing you may find this helpful it's what I used:
Challenge your preconceptions, or they will challenge you.
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