Drupal toolbar not working in dev environments in Firefox? Here's why.

Drupal's toolbar second level of menu options and dropdown not showing? Look for "Uncaught DOMException: The quota has been exceeded." errors, as viewable in the Firefox web console. If you see them, the problem is likely due to sites sharing a top-level domain—which is likely if you are using a local development environment like DDEV, and you working on way too many sites at once—combined with a pretty bad Firefox bug that will be fixed in the next release.

To quote Nathan Monfils:

1. Everything from your public domain (abc.tld) counts against your quota, even if it is in a seemingly unrelated subdomain (e.g. my-app.example.com and intranet.example.com).
2. The quota is not recomputed properly, requiring a firefox restart after clearing your data on other subdomains

Note this may affect all sorts of applications, not just Drupal, when you have them running on multiple subdomains of the same top-level domain. So this isn't just about local development environments (and i dislike that DDEV shares their own top-level domain across all the instances you are working on, and while it can be changed i've accepted its way of doing things so i'm on the same page with other developers by default).

Sure, closing more tabs and restarting Firefox could (predictably) have fixed this—and a lot else that's wrong with me, according to everyone i know—but why do that when i can open more tabs and learn precisely how broken everything around me really is?

I am very happy the bug is fixed and this blog post will be obsolete in mere days! Usually this sort of technical noodlings get relegated to our raw notes, currently hosted through GitLab, but figured at least a few other Drupal developers would want to know what has been going on with their toolbars.

Image credit: "Too Many Tabs" by John Markos O'Neill is licensed with CC BY-SA 2.0.