PDFs are not shown collapsed, makes rooms very slow

Description:

PDFs are always shown as preview. This makes the app very slow when many PDFs are attached to a room.

Steps to reproduce:

Open room with attached PDFs (in MacOS App and Firefox Browser)

Expected behavior:

All PDFs should be shown collapsed

Actual behavior:

All PDFs are shown as preview, not collapsed. The room does not show the bottommost message, you find yourself somewhere in the middle (this might be the correct position if all PDFs would be collapsed). Sometimes the PDF are shown upsidedown.

Server Setup Information:

• Version of Rocket.Chat Server: 1.1.3
• Operating System: ubuntu 16.04
• Deployment Method: snap
• Number of Running Instances: 1
• DB Replicaset Oplog:
• NodeJS Version: v8.11.4
• MongoDB Version: 3.4.20

Client Setup App

• Operating System: macOS 10.14.6
• App Version: 2.15.3
• Installation type: App Store

Client Setup Browser

• Operating System: macOS 10.14.6
• Firefox 68.0.1

Additional context

The "Auto Load Images" setting is false, "Save Mobile Bandwidth" is false and "Collapse Embedded Media by Default " is true

Workaround in Settings - Layout - Custom CSS:

.attachment-canvas{
	display:none !important;
}