To a degree I don't get this 'not a fan favourite'. At the match the crowd adore him and constantly sing his song (which he loves). He might not be everyone's favourite player but that's more because we have a whole team of loveable players and loyalties amongst fans are divided. We've not seen that since we dominated English & European football.
Quite, I don't really get the racial/cultural aspect being a reason at all. He's a great player and probably one of the first names that gets printed on the back of kids shirts.
Mane is a Senegalese Muslim, it has zero bearing on what people think of him as a player.
I'd put it down to two subtle, simple differences between the two. Mane is all smiles and has a positive demeanor, he's not particularly greedy on the pitch, not to the point where it's been mentioned as a problem, he plays for the team and he's a crucial part of that, without it ever having been the case that he carries us and he knows it. Whereas Salah is alot more single minded, to the point where his body language makes it immediately evident there is a problem. Not that Mane hasn't thrown the odd tantrum too, but I feel he's been alot more patient at times before snapping, whereas Salah has repeatedly gotten away with being a bit more selfish, while evidently sulking when things don't go his way.
It's almost like a slightly less obvious version of Michael Owen, when it comes to Salah. Owen was a more self focused and career minded player than Fowler (for example) and that had a slightly negative effect on his relationship with the fans. Not that he wasn't adored too, but you always got the impression that he was much more of a careerist who was focused on individual triumphs above what the team achieved.
I have always had that same niggling feeling with Salah. I love him as a player, I think he's brilliant to watch and a generally, genuinely nice personality, I thought the same about Owen, (yeah he was boring, but not malicious), but always had that sinking feeling that he would one day leave us for what he considered a bigger and better club, or just simply a new challenge. Salah will probably do the same, but he's won everything with us. It'll be a shame when/if he does eventually go, but it won't be a surprise one bit.