I have been using ID in Chrome on a Mac (10.11.6) with no problems. For the past few days all features are shown with 1 pixel wide lines instead of the regular form - e.g. roads, building outlines.
Firefox 43.0.4 has no problems
I just upgraded Chrome (now 67.0.3396.62 (Official Build) (64-bit)) and the problem persists.
Looking at the browser console errors I see
Failed to load resource: net::ERR_FILE_NOT_FOUND
blob:https://www.openstreetmap.org/b3aebe27-63c2-4997-b4f8-26ecb9ebed76
I have restarted the browser and machine - no change
I spoke too soon - Firefox was working fine but just developed the same problem - updated it to v 57.0.1 - still showing the problem...
Here is an example

Sounds like you're in wireframe mode, try pushing W .
That was it ! thanks - must have hit it by mistake - it's right above the S
I'm closing the issue
per chat with @JamesKingdom , we should add a visual indicator somewhere to remind users that they are in wireframe mode, since it is easy to accidentally toggle it 馃憤
Most helpful comment
per chat with @JamesKingdom , we should add a visual indicator somewhere to remind users that they are in wireframe mode, since it is easy to accidentally toggle it 馃憤