Never considered Firefox a good browser, even back when we only had IE, Firefox was unstable and resource hungry (only fanboys can claim otherwise).
It has been getting worse with each rewrite not to mention the poor decisions from Mozilla itself.
There's a reason Chrome got so much traction when it arrived on the market, and wasn't solely due to the fact it was from Google, but was the first and proper alternative to IE (fast and stable, contrary fo Firefox).