Making crossdomain ajax requests with addons for Firefox

I'm a bi开发者_运维知识库t confused about how you can or cannot make crossdomain ajax requests in addons for Firefox. Addons such as LastPass and Xmarks suggest you can do it, however when I try to google how you do it, everyone seem to say you cannot, unless the user has set a preference in the settings of Firefox. If crossdomain isn't possible, then how do Xmarks, LastPass and other addons handle the communication with theirs respective servers?

You most definitely can make cross-domain XMLHttpRequests in Firefox add-ons.

There's a reference to it here: https://developer.mozilla.org/en/Extension_Frequently_Asked_Questions#I_cannot_initiate_an_XMLHttpRequest_from_my_extension