I used Waterfox about 8 years ago, since standard Firefox didn't provide 64-bit Windows releases. After about a year, I got frustrated that it was skipping every other release, so I went back to standard Firefox. Between using NoScript (blocking most scripts), and benchmarks showing 64-bit wasn't much (if any) faster, I didn't notice standard Firefox being slow.
I used Waterfox about 8 years ago, since standard Firefox didn't provide 64-bit Windows releases. After about a year, I got frustrated that it was skipping every other release, so I went back to standard Firefox. Between using NoScript (blocking most scripts), and benchmarks showing 64-bit wasn't much (if any) faster, I didn't notice standard Firefox being slow.