See this
screenshot. Firebug's debugger just encountered a breakpoint, but the "run", "step in", "step over" buttons are inaccessible. That means there's no way to continue execution of the scripts. What's wrong? Firebug 2.0.9 on FF 38.0.1 (tried two different Windows install, same behaviour, Linux FF 37 with 2.0.9 -- same behaviour as well).
Also, upon encountering the breakpoint, the yellow triangle won't appear, but when you switch to console tab and back, it will appear. This definitely looks like a bug to me.
Borek