[BUG] The extension doesnt work on Burp Pro v2026.1.4

[PartyManCZ]

Describe the bug
It looks like due to recent changes regarding Burp and its UI the extension is now broken and doesnt work. In previous versions the Customizer was acting strange in some windows (random red background colors, some parts "uncustomized") and now in Burp Suite Professional v2026.1.4 it doesnt work at all. The tab doesnt show, nothing gets "customized" and the error log shows this error:

java.lang.ClassNotFoundException: com.formdev.flatlaf.extras.FlatUIDefaultsInspector at java.base/java.net.URLClassLoader.findClass(URLClassLoader.java:377) at burp.Zc3r.loadClass(Unknown Source) at java.base/java.lang.ClassLoader.loadClass(ClassLoader.java:490) at com.coreyd97.burpcustomizer.BurpCustomizer.initialize(BurpCustomizer.java:73) at burp.Zceo.ZI(Unknown Source) at burp.Z_2p.Zz(Unknown Source) at burp.Z_29.lambda$initialiseOnNewThread$0(Unknown Source) at java.base/java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:545) at java.base/java.util.concurrent.FutureTask.run(FutureTask.java:328) at java.base/java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1090) at java.base/java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:614) at java.base/java.lang.Thread.run(Thread.java:1474)

To Reproduce
Steps to reproduce the behavior:

1. Update / Downgrade to Burp Suite Professional v2026.1.4
2. Download the Burp Customizer extension
3. Observe the described non-functionality
4. See error

Expected behavior
The extension should load a tab on the top, where you can select a motive. Upon selecting and applying the colors of Burp Suite should be modified.

Versions:

• OS: Kali GNU/Linux Rolling VERSION 2025.2
• Burp Suite Pro v2026.1.4