One-Click Postage (and possibly, more features of XKit) when using Firefox 30 (“Nightly”) is not working right now. It’s not XKit’s fault.

For example, If you’ve noticed, when clicking on the reblog button or trying to create a new post, Tumblr opens the now-ancient reblog page, and not the regular “light popup” version thats been in use for over a year and half now.

Upon closer inspection, I’ve discovered that Tumblr servers return a “Not Found” page when trying to use their /svc/ API (that XKit and Tumblr itself uses). This, combined with the re-appearance of the old page suggests that Tumblr servers does not recognize Firefox 30 so it treats it as a “very old browser”, denying access to the /svc/ API requests.

Unfortunately, there is absolutely nothing I can do about this. I suggest using Chrome or downgrading to a non-nightly version of Firefox, at least until they fix this.

PS: Please do not use a user-agent switcher. They cause more problems than they fix because of various technical reasons.