I'm not sure what you're saying is happening. To uninstall most programs on Macs, you just need to drag the program in Applications to the trash. (That leaves some files behind, but it's usually not a big deal.)

But before uninstalling Standalone, you should first check the location of your Zotero data directory. If you installed Standalone first, your data directory might be within a Standalone-related directory, and while it's not necessary, it'd be a good idea to move it to the default Firefox location instead.

While moving data directories around, it's a good idea to temporarily disable auto-sync in the Sync pane of the preferences, so do that first in both Standalone and Zotero for Firefox.

Once you've made sure that Zotero for Firefox is using its default location (or a custom location of your choosing elsewhere on the system, but not within the Standalone profile directory) and you've moved your old data directory there (if necessary), you can just drag Zotero in Applications to the trash and re-enable auto-sync in Zotero for Firefox.

Good morning,
I have been trying to uninstall Zotero Standalone from my iMac for a week now with no success. Mac High Sierra 10.13.4

I dragged the app into the trash
I used spotlight to search out and delete all Zotero files and directories

Please, I want Zotero FULLY UNINSTALLED from my computer. I am losing my patience with this. It should already be gone. I am tired of reading forum entries like these, following the directions, and not getting results.

@Harrumphulous If you are concerned about removing all of the supporting files when uninstalling applications, I recommend you use the CleanMyMac program and its “Uninstall Completely” tool. Zotero doesn’t behave any differently than any other program on Mac. As Dan says, we would need more details to help you further.

Again, Zotero is just like any other Mac program--this would have been an issue with your computer, not Zotero.