[openstreetmap/openstreetmap-website] JS crash when WebGL is disabled (Issue #6240)

[Jacob Nevins]

jtn20 left a comment (openstreetmap/openstreetmap-website#6240)

I've run into a more severe symptom, with (I suspect) the same root cause: in a browser with WebGL disabled, after switching to one of the WebGL-based layers, the map on the openstreetmap.org website can end up entirely unusable (even after reloading the page or restarting the browser), until I manually delete a cookie; there's no way to switch back to a tile-based layer.

Unlike the other reporters, in this scenario I'm running regular Firefox (Debian's firefox-esr, 128.13.0esr), but with `webgl.disabled=true` set manually in `about:config`.

When I normally visit openstreetmap.org (with the default layer, or another tile-based layer in the cookies), everything seems to work fine. If I peek at the console, no complaints about WebGL.

If I open the "Layers" sidebar, the previews for "Shortbread" and "MapTiler OMT" are absent (grey rectangles), but that's to be expected. If I'm watching the console at this point, I see "Failed to create WebGL context: WebGL is currently disabled", and an "Uncaught Error" mentioning this; but this doesn't seem to obviously break any functionality; the slippy map can still be moved/zoomed, the layer previews update, etc.

If I then click on "Shortbread" in the Layers sidebar, the slippy map fails to display, which is also expected given my configuration.

If I then drag the (non-functional) map a bit, my `_osm_location` cookie gets updated to a value with a `|S` suffix, permanently selecting the Shortbread layer. (I think this dragging step probably explains why the previous reporters, using Librewolf, didn't have the same experience as me.)

At this point I am stuck: clicking back to a tile-based layer such as "Standard" has no effect; on reloading openstreetmap.org, the map is grey (and the browser console shows various errors to do with the absence of WebGL immediately), and the Layers sidebar, when opened, has no content (clicking to Share and then back to Layers appears to then populate it, but the buttons still don't do anything).

The only way I found to get openstreetmap.org back to a working state was to (using developer tools) manually delete the `_osm_location` cookie; I couldn't find a way to do it through the normal UI.

(I suppose that when a WebGL-based layer is already selected via cookie on page load, the errors from the lack of WebGL support are early or extensive enough to break things like the Layers dialog entirely; but I don't know.)

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