A while back urlLauncher suddently and silently stopped working after an update to version 9.16, and I'm sure I’m not alone with this. The culprit is the upstream itself, as can be seen in their changelog:
- INCOMPATIBLE CHANGE: renamed urlLauncher resource to url-launcher.
So, to fix this just change
URxvt.urlLauncher: browser line to
URxvt.url-launcher: browser in your