You can uninstall Zotero just like any other Firefox extension by going to the Firefox menu Tools→Add-ons→Extensions tab, selecting Zotero, and clicking “Uninstall.”"
Keep in mind that uninstalling Zotero does not delete your library. Large libraries can take up quite some space (especially if you have attached large files to your items). To also remove your library (this will mean losing your data!), follow the instructions found at the link below to find the location of your library:
Upgrade Storage
"How do I uninstall Zotero?
You can uninstall Zotero just like any other Firefox extension by going to the Firefox menu Tools→Add-ons→Extensions tab, selecting Zotero, and clicking “Uninstall.”"
Keep in mind that uninstalling Zotero does not delete your library. Large libraries can take up quite some space (especially if you have attached large files to your items). To also remove your library (this will mean losing your data!), follow the instructions found at the link below to find the location of your library:
http://www.zotero.org/documentation/frequently_asked_questions#where_does_zotero_store_my_references_and_notes