For various reasons, I have an account on my system named "thisnameislongandbreakscrontab" (see the bug reports for vixie-cron for that whole sordid story). At any rate, consequently I have the directory /home/thisnameislongandbreakscrontab on my system. Mozilla refuses to load files from there using the Open File command; in the dialog box, that directory doesn't even appear to exist. Hopefully the limitation is in Mozilla and not in the GTK libs....
Should be fixed in 0.9.1 which will show up in rawhide shortly.