For those of you who are using beta versions of Firefox 4, I have just put a version of Wizz RSS online that will install on 4.0b5.
The scroll bar weirdness persists, but the latest news on Bugzilla ( https://bugzilla.mozilla.org/show_bug.cgi?id=584703 ) indicates that a fix has been landed for testing. Maybe 4.0b6 will include the fix.
You can get Wizz RSS 4.0 here

I have not been able to figure out how to post bugs in previous version, so I am reporting it here:
I have Wizz RSS 3.2.0.0 and I just upgraded to FF v3.6.9.
After the upgrade, the URL is no longer showing in the address-bar and the back/forward buttons stopped working.
If I disable Wizz RSS, Firefox works fine again. I tried uninstalling /reinstalling Wiz RSS, but the problems return as soon as Wizz RSS is enabled.
Some more info. It appears that there is an incompatibility between Wizz RSS and Tab Mix Plus (v0.3.8.5pre.100907a), but only after upgrading to FF 3.6.9.
If I disable either Wizz RSS or Tabmix Plus, FF works normal again.
Hi Eric,
It is very possible that conflicts exist between Wizz RSS and other Firefox add-ons.
I’ve been using Firefox 4 beta for a few months, so I don’t know if I’ll be able to replicate the problem, but I’ll install Tabmix Plus and see if I get the same funny behavior. If I can replicate the problem, and can track down its cause, I’ll fix it and post a followup comment on this blog.
I’ve just tried to install Tab Mix Plus. It isn’t available for Firefox 4.0b5. I don’t really want to run two versions of Firefox, and I don’t want to revert to Firefox 3 either.
OK, I found a version of Tab Mix Plus that installs on Firefox 4.0b5 – 0.3.8.5pre.100907a
I see what you mean. Firefox goes crazy when both add-ons are enabled. It seems to me that the problem might be related to the use of PlacesUtils. I can’t disable PlacesUtils in Wizz RSS – It’s a standard utility library that ships with Firefox – because Wizz RSS will stop working altogether.
Hmmmmm… I think we are going to need help from the Tab Mix Plus developers to resolve this one. I found an overlay in the Tab Mix Plus code that messes with the Wizz RSS event listeners. I’ve no idea why Tab Mix needs to do this, so I guess we’ll need the Tab Mix developers to explain what is going on.
I have posted comments about the issue in the TMP Forum:
http://tmp.garyr.net/forum/viewtopic.php?p=44220#44220
Will you be contacting the TMP developer directly?
TIA!
Going back to an older version of TMP resolved the issue: tab_mix_plus-0.3.8.5pre.100830b.xpi
I hop to fix the incompatibility soon.
the reason Tabmix need to change some Wizz RSS code is to prevent it from load new address in locked tab.
the best way is to do the check in Wizz RSS.
if topWin().TMP_whereToOpen(true).lock is true open url in new tab.
Thanks onemen