Looks like a problem with accessing local fonts and Firefox has switched to a last resort font that displays all glyphs as a '?'. You can check in the <b>Rules</b> tab in the right panel in the Inspector what font-family is used for selected text. You can check in the <b>Fonts</b> tab in the right panel in the Inspector what font is actually used because Firefox might be using a different font than specified by the website. If the Fonts tab is hidden, click the down arrow at the right end. *https://firefox-source-docs.mozilla.org/devtools-user/page_inspector/how_to/edit_fonts/ In Firefox 119 Fingerprinting protection has been added to Enhanced Tracking Protection in Strict/Custom mode (Suspected fingerprinters) what affects accessing local fonts. *https://support.mozilla.org/en-US/kb/enhanced-tracking-protection-firefox-desktop To include user installed fonts, modify this pref on the <b>about:config</b> page: privacy.fingerprintingProtection.overrides => -FontVisibilityBaseSystem,-FontVisibilityLangPack You can open the <b>about:config</b> page via the location/address bar. On the warning page, you can click "Accept the Risk and Continue" to open about:config. *https://support.mozilla.org/en-US/kb/about-config-editor-firefox

Does it still happen in [[Diagnose Firefox issues using Troubleshoot Mode|Troubleshoot Mode]]?