tkarpinski/SignalR — comment on commit 2854deae0b46958b0fae814f0c32404bf81b5574
File:  line 0
By tkarpinski:

It appears that intelligent guess works differently in Firefox 9 and 10 depending on whether the request is to a local resource vs a remote resources. Chrome parses the response as JSON whether the request is local or x-domain whereas Firefox will parse the response as JSON on a local, but on cross-domain it will be left as a string. forcing the dataType will address this issue.