XHR requests don't load when rewritten by HTTPS Everywhere (was: Rulesets affecting only XHR requests may not appear in the context menu.)
HTTPS Everywhere has some fairly janky code for figuring out which window a request is associated with, so that it can populate the context menu correctly. The association process doesn't work with XHR requests made by script. Usually that doesn't matter. Occasionally, it does. For insance: legacy/trac#7503 (moved).