those two steps seem to contradict themselves
The idea is not
to set any browser as default from within
the browser itself. I know it is confusing and sounds counter intuitive but that's how it works here.
So just change browser in XFCE (Settings -> Settings Manager -> Preferred applications -> Opera) and make sure no browser is set to default in the browser itself (in it's preferences). If a browser asks if you want to make it the default then answer NO.
Hope this clears it up for you.
Ok that makes sense, and we are tantalizingly close.
I did the XFCE settings thing a long time ago and it didn't make a difference.
Neither browser asks me anything at startup.
After your post, I looked inside FF to see if there was some way to "unset" it as the default.
From what I can see (pic 1 below) FF only has the option to set as default (not unset).
So (for the heck of it) I checked the box that says "always check if ff is your default browser".
I didn't think that it would prompt me at startup because FF seems to be stuck as the default browser already.
However when I restarted FF it did indeed ask me if I want FF as the default browser (pic 2 below).
So I selected "not now".
However nothing has changed, everything still opens in FF.
Did a reboot as well, no diff.
ummm, please don't say "uninstall FF".