While officially these more secure and later versions of Firefox are "not supported" for the vSphere 5.0 web client, there are so many security holes in these older revs, that VMware really should step up the game here.
We started getting user reports who had upgraded to Firefox 23.x about severe startup delays. Here's the info below on the PD submitted to VMware. Case is open but doubtful on resolution beyond the "it's not supported answer.."
Looks like some version later than FF 21.0 is the culprit. Something done to FF between 21.0 and 22.0 induces the 4 minute startup delay we are seeing with at least 3 versions of Adobe Flash per SR. Presented with #1502 (timeout error I think).
When using IE9 w/ webclient,, we do NOT experience these "timeout / error" issues going to same vCS systems.
Windows 7 Pro
I've also disabled all plugins etc on FF and it has no impact.
FF versions: 23.0.0, 23.0.1
Adobe Flash version: 11.8.800.168, 11.8.800.94, 11.7.700.724
PD results..
Latest Chrome --> Works fine w/ webclient no 4 minute hangs..
IE 9 + Adobe Flash (last 3 versions) --> Works fine.
Firefox backleveling..
Firefox 20.0 --> Works, no hangs, login OK, works fine after login
Firefox 21.0 --> Works, no hangs, login OK, works fine after login
Firefox 22.0 --> has 4 minute startup hang w/#1502 timeout error, then works OK after login
Firefox 23.0 --> has 4 minute startup hang w/ #1502 timeout error, then works OK after login
Options for now, see above:
To backlevel FF
1) Remove FF (add/remove)
2) Reboot
3) DL and install from this listing.. --> <http://download.cdn.mozilla.net/pub/firefox/releases/>
Cheers. GC Mobley