I am using SharePoint 2010. I know that IE is the supported browser for uploading multiple documents. Wanted to know if there is any way to use the upload multiple documents in other browser like chrome, Firefox or edge? Whether be it extensions or other means? Thank you. This is a link to show how to enable multiple downloads for IE only
The other way to open document library in explorer is by running command
file://sharepointaddress/sites/docsites/doclibraryname in windows run. This didn't work if you put it in SharePoint 2013 link, I had tried it.
After you open that explorer windows, you could just copy and paste multiple files to it.