Well this is a bit strange about 3-4 months ago I started having problems with zimbra web client on firefox. Basically what happens is that when it receives new mail the entire system freezes for about 1-5 minutes or worse if several emails are received. I have not worried about it till recently when a couple or users told me they were having similar problems. I am the sys admin for a small company and figured I had corrupted my account some how or firefox's profile. Luckily most of my users are on Thunderbird and only a few use the web client exclusively, so maybe its been happening all this time.
I did some tests and I am still stumped. Out of the 20 or so that use the web client regularly 3 are having this trouble [including my system]; incoming mail freezes system for 1-5 minutes, high activity on cpu, no response from system till firefox unfreezes. I have uninstalled firefox and reinstalled it, deleted profiles, ran firefox in safe mode, still the same. This problem looks like its isolated to a few systems because I have checked mail fine on a several Macs [10.4.11 and 10.5.6] and other XP systems and it works fine.
It seems like it might be an account problem because using a different account on the same problem system firefox works fine. Firefox also works fine if my account is accessed in standard mode so maybe its AJAX??
On the same machine my zimbra account works great on IE7, SeaMonkey and Chrome. I have also done a re-indexing of the account.
This has me a bit stumped has anyone seem anything like this or could advice what else to try or look for?