Vimium extension displays link hints in uppercase even when lowercase is selected in settings

Hello,
I'm using the Vimium extension on Ubuntu 24.04 with the Vivaldi browser (Chromium-based). Despite selecting lowercase letters in the "Characters used for link hints" section, the link hints are still displayed in uppercase. This behavior occurs when I press "f" to activate link hint mode.
I've included a screenshot of the settings with the entered lowercase letters and an example webpage with uppercase link hints to demonstrate the problem.
The following information might be helpful for debugging:
Vivaldi browser version: [insert your version]
Ubuntu version: 24.04
Vimium extension version: [insert your version]
Steps to reproduce:
Open Vivaldi browser on Ubuntu 24.04 with Vimium extension installed.
Navigate to any webpage with links.
Press "f" to activate link hint mode.
It would be great if this issue could be fixed, as it affects the user-friendliness of the Vimium extension. If you require any further information, I'm happy to help.

Start by reproducing the issue in Vimium on Ubuntu 24.04 with Vivaldi: enter lowercase characters in the link-hint settings, open a page with links, and press "f". Trace the link-hint display path and verify that the configured lowercase characters are rendered unchanged when the fix is complete.