At our office we have a Google Drive which we use to share files with our affiliates. However some of our employees aren't shown thumbnails for the files, but on other computers there's no problem. I've already tried to update their browser (IE) and installed another browser (Chrome), but no change. All settings and plugins seem to be the same as on a pc where the thumbnails are shown. Not that our employees have limited internet access. Are the thumbnails created by an external site which they have to be able to access or is it something else?
AFAIK, no, thumbnails are not created by an external site, but Google uses a lot of websites to host their services. I don't know the specific one for thumbnails but to avoid this and other problems consider to unblock all the ones listed in the help article regarding regarding the firewall and proxy settings for Google Drive. Below is the link that article and the current content.
In order for users on your network to access Google Drive on the web, Google Drive for Mac/PC, and Google Docs editors, your firewall rules should connect to the following hosts and ports. Otherwise, users may be blocked or denied access from these services.
For the following hosts, [N] means any single decimal digit and * means any string not containing a period.
- talk.google.com:5222/XMPP (needed only for Google Drive for Mac/PC)
- The IP addresses that various domain names resolve to don't necessarily fall within any given address range.
- Other Google properties may use the IP addresses that Google Drive uses.
- Techniques that Google Drive uses to connect to Google servers depend on the browser, browser version, networking conditions, etc.
- Even if you don't currently observe activity at the addresses listed above in a particular Google product there could be future activity.
- Google Drive for Mac/PC supports all unauthenticated proxies that are configured by the operating system.
- Google Drive for Mac/PC supports only DNS-based distribution of PAC files. PAC distribution over DHCP is not supported.