When accessing my Google Drive on Firefox and opening a shared folder containing picture files, the files can only be downloaded, not previewed. This is the case for heic files (I am working on a PC; files were uploaded from an iPhone) and jpg files. The latter can be opened in Google Docs; the former can only be viewed using an outside app. In both cases, the files must be viewed outside the drive. The file previews appear (both on the icons and if the files are double clicked) when opened in Microsoft Edge.