ZoteroPreview plug-in discontinued??
                    Hi, I installed this plug-in several times. It works a while, then disappear. 
When we check the extensions list within the standalone version, this plug-in has the statut "discontinued". The extension must be deleted and then re-installed each session and even if it works it's very slow.
                
                            When we check the extensions list within the standalone version, this plug-in has the statut "discontinued". The extension must be deleted and then re-installed each session and even if it works it's very slow.
 Upgrade Storage
https://www.zotero.org/blog/zotero-7/