Firefox issues

[NoDoze]

I'm a network admin here...and I'm having some users experiencing issues with firefox 3.5.2....IE works fine.

So far only two people are having this similar issue.

When its their first time logging into the zimbra web ui for the day, or the first time anytime after a restart, they are unable to create a new email.

- their browsers are set to open a new compose window in the same window, not in a new window.
- it ONLY occurs with the new email tab, or even when clicking the pull down menu and clicking new email. new claendar, new contact, ect, all work ok.
- The ONLY way to fix it is to close the browser window and reopen it, OR change the theme, then the new email will work.

I've created a new windows user; cleaning out the cache, history, ect for the browser; tried different themes; and tried all default settings - all made no difference.

Release 5.0.16_GA_2921.RHEL5_64_20090429051405 CentOS5_64 FOSS edition

Any ideas?