Uninstall works well with MSI bundles. To be honest, I haven't tested any other option.

There will be a couple of things...

#1 - You need to make sure the "Uninstall Tab" has the Actions for actually CALLING the Uninstall.

For FireFox it will be "C:\Program Files\Mozilla Firefox\uninstall\helper.exe" with /S on the command-line.  Be sure to set to Dynamic Adminsitrator for permissions.

https://support.mozilla.org/en-US/kb/silently-install-uninstall-firefox-enterprise#:~:text=How%20to%20Uninstall%20Silently,the%20command%20line%20parameter%20%2FS.

The Windows Registry Often contains the Uninstall Commands for uninstalling Apps, which you can use to add in the necessary calls.  ZCM won't magically know what the Uninstall String is for Application installs.  

For MSIs, ZCM will try to add some Uninstall Commands, but the built in defaults are inferior to getting the actual uninstall commands since the default method requires the original source while the Registry Parameters would not.  Who wants to download 2GB of install files to uninstall when its not necessary.  

Thought should be put into the "Uninstall Actions" just as one puts thought into the "Install" actions.

#2 - Since you modified the App to ADD Uninstall commands, it would not be the version that was installed.  ZCM can not presume that the different versions need the same uninstall string so you may have to install it again before the uninstall worked....likely not what you want in this case since you only goal is to remove....not update the app so in the future it could be uninstalled if desired.

#3 - SInce you had not configured Uninstall for the version you deployed....The simplest would be to just create a bundle to directly call the Uninstall if FireFox is on the system.  Go back to Item #1 and put that under "Install" or "Launch"  actions instead of "Uninstall" actions.

We are using an MSI, but the default Undo Actions weren't doing anything.  So I added the "C:\Program Files\Mozilla Firefox\uninstall\helper.exe" with /S on the command-line and still nothing.  That's why I was confused on why it wasn't working.

I did create a separate Launch bundle and assigned it to a few machines and that seemed to work just fine, which is what I have done in the past, so will just stick with that.  Thanks for the information, though.

If you manually run that command does it work?  If so, it should work in the ZCM bundle.  I only recently started using the Uninstall option, but it works fine.  For some bundles, the "Undo Install Actions" work as is.  For other bundles, I have had to disable that and use Launch Executable and File Removal to clean things up.  You just need to figure out the command necessary to uninstall the product, enable uninstall, and put the commands in there.

Yes, it does work and when I put in the Launch action, it works, as well.  I'm going to look at it a little more today and see what I can find.

Under Configuration > Device Management > ZENworks Explorer Configuration, there is setting to choose if unassigning bundles even runs the uninstall step, and if so how many days it waits until that happens.

Since you are knew to use it....always be careful about the automatic uninstall when you remove the assignment.  Sometime that can kick in unexpectedly.

I had a customer Create a New Office Bundle instead of changing the version to tweak some thing.  He then unassigned the old and assigned the new.  A week later office was uninstalling on all his PCs and he did not know why....the delay made him forget the change he made in assignments.

Being able to tell the bundle to uninstall is great....but historically i find few people get mad when old unneeded software is on their PC but get really upset when you unintentionally uninstall something they actually need