You can't break on functions that have breakpoints that get called from the Drosera console.
Bug 10200 has a fix that prevent callback reentrancy. I thought this would prevent cases where you call a function from the console and expect it to break on a breakpoint in them, but this appears to never have worked even without that change.
The worst thing about this is that it isn't documented anywhere, unless you looked for this bug report like I did. I was trying out the WebKit debugger and was assuming the breakpoints were just broken. Running a function from the console is an obvious way to test code and to get to breakpoints. I don't think it's a minor bug.
This is no longer reproducible. However, it would be nice if there was a test for it. For that, I filed a new bug: https://bugs.webkit.org/show_bug.cgi?id=126845