contact list no longer showing with latest Waterfox Classic (2022.06)

Describe the bug

In the latest Waterfox Classic web browser, the Contacts page stays empty – only the header is shown. Cross-Checking with Waterfox G4, here everything shows up as expected.

Steps to reproduce

1. Log in to Nextcloud
2. Click on the icon for the Contacts app
3. See an empty page with just the navigational header

Expected behavior

Contacts list would show up

Actual behavior

No contacts shown at all. Inspector shows this:

instead of (as in G4):

Contact version

4.1.1

Operating system

Linux Mint 20.3

PHP engine version

PHP 7.4

Web server

Apache (supported)

Database

MariaDB

Additional info

In the browser console, I see a lot of CSS warnings like

Missing closing ‘)’ in negation pseudo-class ‘[’.  Ruleset ignored due to bad selector. contacts:1:37
Unknown property ‘color-scheme’.  Declaration dropped.  contacts
Unknown pseudo-class or pseudo-element ‘-webkit-scrollbar’.  Ruleset ignored due to bad selector.  6062-aa19-server.css:1:2023
Unknown pseudo-class or pseudo-element ‘-webkit-scrollbar-track-piece’.  Ruleset ignored due to bad selector.  6062-aa19-server.css:1:2066
Unknown pseudo-class or pseudo-element ‘-webkit-scrollbar-thumb’.  Ruleset ignored due to bad selector.  6062-aa19-server.css:1:2127
Error in parsing value for ‘position’.  Declaration dropped.  6062-aa19-server.css:1:2416
Unknown property ‘user-select’.  Declaration dropped.  6062-aa19-server.css:1:2626

(list is pretty long, I can attach it if it helps), followed by things like

No OC found  main.js:160:149063
JQMIGRATE: Migrate is installed, version 3.3.2  main.js:986:933
jQuery is deprecated: The global jQuery is deprecated. It will be removed in a later versions without another warning. Please ship your own.  globals.js:62:15
$ is deprecated: The global jQuery is deprecated. It will be removed in a later versions without another warning. Please ship your own.  globals.js:62:15

But maybe a key error is

SyntaxError: missing : after property id      contacts-main.js:2:3869133

Maybe some incompatibility with the Javascript engine (I vaguely remember GitLab had some similar issues a while ago and they got them fixed). Funny to see is OC.Util.relativeModifiedDate is deprecated and will be removed in Nextcloud 21. See @nextcloud/moment from util.js:135:11 (I'm no longer on Nextcloud 21; at the moment I am on 22.2.9 with updates to 23/24 planned soon™).

Currently, as a work-around, I can copy the Contacts URL to some other browser (e.g. Waterfox G4), but Classic is still my main browser (and still receiving updates), so I'd appreciate a fix if possible. Should further details be needed, I'll of course do my best to provide them. Thanks in advance!

Reproduce the empty Contacts page in Waterfox Classic and inspect the reported SyntaxError in contacts-main.js, alongside the browser console output. Compare the behavior with Waterfox G4; the work is done when the Contacts list renders in Waterfox Classic without the reported failure.