First off, ignore the Savage Species anthro-stats, as they're a really bad adaptation IMO.
Start by taking a look at the actual animal.
Foxes are small, slender, agile animals that are nocturnal hunters. So, probably a penalty to STR and/or CON, and a bonus to DEX, and low-light vision. (As a monstrous humanoid, anthros automatically get darkvision for free, but this is one of the things I disagree with about the Monst. Humanoid type.) They have big ears and sharp hearing, and a good sense of smell. Teeth are sharp, but the jaws are not all that strong. Like canines, they have clawlike nails, but unlike true claws these are not strong enough for claw attacks. (They're attached to the skin, like human fingernails, rather than anchored to the fingerbones like true claws.) Foxes have attractive fur which is fairly thick for their size.
Second, look at the animal as protrayed in legend and stereotype.
Foxes are almost universally regarded as tricksters - clever, fast-talking, and charismatic. Since they are opportunistic scavengers as well as hunters, and their small size and slender build lets them slip through small gaps in walls and fences, they have acquired a reputation as thieves. So, probably a CHA bonus, possibly an INT bonus, and favored class either rogue or bard.
So, as a starting point we have:
+2 DEX
-2 CON
+2 CHA
+2 Listen checks
Cold tolerance 1 (fur) (cf Frostburn)
bite: 1d4 slashing
Acute Sense of Smell: this is basically a nerfed version of Scent, weakened for LA+0 races, as seen in the Lupin race in Dragon Compendium. Basically it gives:
+5 on Spot vs Disguise checks to penetrate a disguise, if within 5 feet and if you're familiar with the target's scent;
Free-action DC 10 WIS check to pinpoint an invisible or Hiding creature within 5 feet;
+2 on Survival rolls to track
The above ought to be acceptable as an LA+0 race. Giving them full Scent and/or a +2 to INT would bump them up to LA +1.