javascript - onunload Ajax not always working (Chrome extension) -

i writing chrome extension, , want fire post submission right before client unloads webpage.

to this, tried using both window.onunload , window.beforeunload. when page unloads, use jquery.ajax make post submission. include async: false in request.

with this, post triggers websites upon unloading. however, there websites don't seem firing unload function!

sites aren't triggering me include (just out of testing): http://www.yahoo.com , http://www.paulgraham.com/ds.html

i stuck. there specific sites aren't firing i'm not accounting for? can make function trigger universally?

thank you!