[Bug]: Broken cyrillic encoding on 4pda.to (maybe other sites too)

[diadark7]

Pre-Submission Checklist

• I have checked the existing/closed issues to ensure this issue has not already been reported.
• I am using the latest supported version of the browser.
• I have tried disabling all browser extensions/add-ons to rule out interference from these.
• I have tried clearing the browser cache and cookies.
• I have checked with a new profile and the issue still occurs.
• I have provided detailed step-by-step instructions on how to reproduce the issue.
• I have included relevant screenshots or console outputs.
• I have checked that this problem is not occurring in the latest version of Firefox ESR.
• This issue is specific to this browser and does not occur in other browsers.

Bug Summary

Broken cyrillic encoding on 4pda.to - some elements of site and when search cyrillic symbols becomes abracadabra

Reproduction Steps

Open site - encode broken

Expected Behavior

Firefox (and Waterfox):

Actual Behavior

Broken Russian encoding on 4pda.to (and in Mercury this bug exists too):

Search:

Screenshots

Browser Version

11.21.0 (64-x)

Operating System

Windows 10 x64 22H2

Additional Context

No response