Do you have full control over the clients which make requests (e.g. it's only AJAX or 3rd party clients written to your api spec - i.e. not browsers making raw

Do you have full control over the clients which make requests (e.g. it's only AJAX or 3rd party clients written to your api spec - i.e. not browsers making raw requests against some of your urls?) I backed away from using content-negotiation for an API, part of which would have served data and part content. e.g. to access file metadata, get /path/to/file with Accept: api/v1 and do a 'normal' GET to get the file contents. I came across some suggestions that some browsers (recent IE I think, unsure) which suggested that cacheing was broken wrt Accept header - which made me worry that people hitting accessing the resource might get the wrong version. I don't know if your api is vulnerable to this, if you've come across the problem or have any deployment wisdom to share.