Cannot download anything. Images/files/website formatting etc.

Boot into Safe Mode according to Start up your Mac in safe mode - Apple Support and see if the problem persists. Reboot normally and check again.

NOTE: Safe Mode boot can take up to 10 minutes as it's doing the following; 

• Verifies your startup disk and attempts to repair directory issues, if needed

• Loads only required kernel extensions (prevents 3rd party kernel/extensions from loading)

• Prevents Startup Items and Login Items from opening automatically

• Disables user-installed fonts 

• Deletes font caches, kernel cache, and other system cache files

To make it easier for us to see the screenshots you post please read the following:

How to take a screenshot on your Mac 

(⌘⬆︎3) Command-Shift-3         Capture the screen to a file

(⌘⬆︎⌃3) Command-Shift-Control-3 Capture the screen to the Clipboard

(⌘⬆︎4) Command-Shift-4         Capture a selection to a file

(⌘⬆︎⌃4) Command-Shift-Control-4 Capture a selection to the Clipboard

(⌘⬆︎5) Command-Shift-5         Invoke new screen grabber

Paste the following command in the Terminal window followed by the Return or Enter key to change the type of screenshot file to jpeg:

defaults write com.apple.screencapture type jpg && killall SystemUIServer

Past the following commands in the Terminal window followed by the Return key to change the save location of screenshots to the desktop.

defaults write com.apple.screencapture location ~/Desktop/ 

killall SystemUIServer

Have you tried a different browser? That happens to me occasionally; it always clears itself up sooner or later. When it does, I switch browsers; Firefox and Safari.