I was working on a Laravel/Statamic site. Out of the blue, Firefox complained that the "issuer certificate" had expired.

I had added the Laravel Valet Self Signed CN issuer certificate a couple of years ago, and now it apparently had expired.

Googling the issue proved to be very difficult, but eventually I found this issue in the laravel/valet repo:

Root CA expires after 730 days without a convenient way to renew it #1103

And it seems that it was fixed in this pull request, where they (correctly, in my book) deemed it a bit silly that this certificate ever expires:

Avoid expiring of root certificate authority #1161

So what I did, was this:

Assuming you are on a recent version of Valet (which you should be!), the expiry date for the new certificate should be set to twenty years in the future. So it's not like it never expires, but by then you really should consider getting a new computer!