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?

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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