Proxy for all sites breaks Kee Browser Extension

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Kee is a browser extension for Firefox. It allows the user to autofill passwords using the credentials from KeePass 2 using an RPC which opens an RPC server on localhost.

When installing the Mullvad Browser Extension and enabling the "Proxy for All Websites" feature, the Kee Browser Extension stops working after a browser restart and can't connect to the KeePass RPC any more. This behaviour only started recently and wasn't the case a few weeks ago before the default proxy was replaced be the "Proxy for All Websites"-switch.

Repro

1. Ensure KeePass and Kee extension are configured correctly and operational.
2. Install Mullvad Browser Extension.
3. Enable the "Proxy for All Websites" feature in the Mullvad extension settings
4. Restart firefox.
5. Watch how the connection between Kee and KeePass doesn't work anymore.
6. It starts working again when disabling the "Proxy for All Websites" feature.

The only workaround is to disable the "Proxy for All Websites" switch, let Kee connect to KeePass, and then enable the "Proxy for All Websites" again.

As I said: this issue only appeared recently and didn't happen in the old versions of Mullvad's Browser Extension

System Info

• Firefox 124.0
• Windows 10 x64
• KeePass 2 2.55
• Kee 3.11.13 (Oct 18, 2023)
• Mullvad Browser Extension 0.9.0
• KeePassRPC 1.16.0