Greasemonkey seems to fail with too many gm_xmhttprequests?

[jeffrey4]

I'm trying to write a script (my first) that loops through some table
rows and gets some data from another page using gm_xmlhttprequests. It
works if I keep the loop to one, but if I try and loop through all the
rows, and therefore have say 10-20 gm_xmlhttprequests, the script just
seems to fail. But if I put an alert inside each gm_xmlhttprequest, and
wait a bit before dismissing the alert, the gm_xmlhttprequest will
succeed and the data gets updated as planned. It seems as if the
gm_xmlhttprequests don't block, or the script keeps executing without
waiting for the requests to finish. I don't have any listeners on the
script, I just want it all to load when the page loads. Also, I looked
at the javascript console and it doesn't have any errors about the
gm_xmlhttprequests.

Any ideas?