STEPS TO REPRODUCE: 1) Start firefox. 2) Open browser console. 3) Set a breakpoint in some code I think should get hit when opening a link from another application. 4) Click a link in my mail client. EXPECTED RESULTS: Link opens in browser, breakpoint maybe gets hit. ACTUAL RESULTS: Link opens in the browser console process, in a Firefox window that gets created there. This is not terribly helpful... ;)

I think this is referring to the Browser Toolbox process, not the Browser Console which is just another window running in the parent process. I can't reproduce it (testing on a local build on osx) but I skipped step 3 since I wasn't sure where to set the breakpoint. Can you give more detail on step 3?

At first I was going to say the BT process needs `-no-remote`, but it appears we already pass that: http://searchfox.org/mozilla-central/rev/1c4901d060e3953e41088c038b62a0c026c1e1fb/devtools/client/framework/ToolboxProcess.jsm#254

Er, sorry, I meant "browser toolbox" throughout, yes. We have too many tools... For step 3, I was setting the breakpoint on http://searchfox.org/mozilla-central/rev/1c4901d060e3953e41088c038b62a0c026c1e1fb/devtools/shim/devtools-startup.js#240

Passing -no-remote will make it actually start a new process instead of reusing the existing Firefox process. I'm not sure it affects what process the OS will target for its "open link in default browser" functionality....