The full scope of the recently-discovered Spectre and Meltdown vulnerabilities is still being determined. It may be that hardware or firmware changes will be necessary to truly remove the danger. However, it’s still possible that operating system and application updates can mitigate the risk sufficiently for most purposes.
The result is Firefox 57.0.4, released on January 4. It’s difficult to know just how helpful these changes will be, but if you use Firefox, you should install this update.