For a long time I've used firefox dev edition because their developer tools have been easier, particularly for editing and re-sending HTTP requests. (Right click "edit and resend" in firefox vs ? in chrome).

Also in firefox you can screenshot not just the whole page below the fold but screenshot any element by right-clicking the element in the elements pane.

It's not up to par with Chrome Dev Tools, but something to keep an eye on is https://github.com/devtools-html/debugger.html (a project run by Mozilla). This has the benefits of being open source and very accessible to developers (because of the technologies & being on GitHub).

It may one day give Chrome a run for it's money.

Edge will probably get time travel debugging first, allowing you to rewind and inspect after something happens. Way better than adding debugger or console.log() everywhere.

There is no better alternative. Or at least there wasn't earlier this year.

I tested several cross-platform browsers in Q1 this year and I always had to go back to Chrome because it's the smoothest dev experience.