FireRed and LeafGreen were the first main-series Pokémon remakes, updating the 1996 original Red/Green (and Blue ) for Game Boy Advance. The “1.0” here is the original North American release (the -u indicates USA), before later revisions patched minor bugs.
: Advanced hacks that change game mechanics (like adding Mega Evolutions or the Fairy type) require the specific memory offsets found only in the 1.0 version. If you are trying to play a hack like Radical Red 1636 Pokemon Fire Red 1.0 -u--squirrels-