The best replacement for firered is leafgreen.

The best alternatives to firered are rated as following:
★★★★★  leafgreen
★★★  emerald
★★  heartgold
  pokemon red
  pokemon leafgreen
  leaf green

Your alternative for firered is not listed? Suggest!
Speaking about firered, one probably shouldn't forget about pokemon ruby.

Other search terms related to firered and their ratings are:
★★★★★ pokemon ruby
You have in mind a companion for firered and it is not yet here? Propose!



Google Trends

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firered
leafgreen
emerald