If I had to guess, I'd say blame Opera (probably silently installed an update that broke stuff?). It's my favourite browser, but a
real bitch to get to properly integrate with other programs. I have a wrapper script that launches it with "opera -nomail -newtab $(url)", maybe try it this way? Can't remember
exactly why I put the "-newtab" in there however.
If you don't want to use a wrapper, setting ExternalBrowser in the ini file's "Advanced" section
might work too, haven't tried it though, so no guarantees.
Code:
[Advanced]
ExternalBrowser="path/to/opera.exe -newtab"