That seems to be premature. Depends what you consider a DevTool. Chrome still has far better profiling/tracing tools for performance analysis. The latest Chrome versions even let you hover over functions and view what the V8 JIT thought of them (e.g. deoptimized and why). Even relatively low hanging fruit, like debugging WebWorkers is missing from FF. I see tons of missing stuff that Chrome DevTools has that FF is missing. It doesn't have something like the Timeline tab for tracking memory/framerate over time. I don't see stuff like HTML5 FileSystem/IndexDB/localStorage browsing. SourceMap support doesn't match Chrome. Etc.

FF seems to do better with the DOM/Designer portion of tooling, but from a JS-heavy coder perspective it seems behind.