All Microsoft Browser Apps Display Their Fonts in Bold

Question

I'm having the same problem that's posted in this thread: https://learn.microsoft.com/en-us/answers/questions/5645033/font-all-in-bold?source=docs

On all my browser Microsoft apps, the fonts of the entire page show up as bold. I'm on a 2023 Macbook Pro, Tahoe OS. The issue started sometime in Dec 2025.

Here are answers to the questions asked in the other thread:

• Does this happen in all browsers or just one (e.g., Edge, Chrome, Firefox)? What are the affected browsers 
  • Happens in Chrome and Firefox, not Safari
• Do non-browser apps (like Word, Teams, or system menus) also appear bold, or is it only web pages? 
  • just the web pages
• Have you enabled any accessibility settings such as High Contrast mode, Increase Contrast, or custom display settings? 
  • No
• Are you using any browser extensions or tools that modify fonts, styles, or enhance readability (e.g., Bionic Reading, Reader Mode)? 
  • No
• Does the issue persist when you open an InPrivate/Incognito window or use a different browser profile? 
  • It persists in Chrome Incognito but not Firefox Private
• Have you installed any custom fonts recently (e.g., Segoe UI or design packs)?
  • No 
• Did this start after a recent update (browser, OS, or Microsoft service)? 
  • I don't believe so

Answer 1

Dear @David Lauer,

Welcome to Microsoft Q&A Forum!

Based on your description, could you please check the Font Book application on your Mac and confirm whether there are any corrupted or duplicate font files, especially Helvetica / Helvetica Bold (TTF)?

I’ve seen similar cases on macOS where a corrupted or duplicated system font (such as Helvetica Bold.ttf) can cause browsers to render all web text as bold.

You can check this by following these steps:

• Open Font Book on your Mac
• Select All Fonts in the left pane
• From the menu bar, choose File > Validate Fonts
• Review the results and look for any fonts marked with errors or warnings
• If you see any corrupted or duplicate entries (for example, Helvetica Bold), please remove or resolve them
• Restart the browser and check if the issue is resolved.

Also, in Chrome browser, please go to Settings > Appearance > Fonts > check San-serif Font. You should make sure that the font in it was not a corrupted font in Font Book. Browsers (Edge, Chrome, Firefox) on macOS may default to sans‑serif fonts for web pages.

If a system sans‑serif font (like Helvetica or Helvetica Bold) is corrupted or duplicated, browsers may render everything as bold.

Please see this article to validate font and solve duplicate font: Install and validate fonts in Font Book on Mac

Note: This information is provided as a convenience to you. These sites are not controlled by Microsoft, and Microsoft cannot make any representations regarding the quality, safety, or suitability of any software or information found there. Please ensure that you fully understand the risks before using any suggestions from the above link.

I hope this information can give you some insights and please let me know how things go on your side as your update can also assist others in the community who may be facing the same issue.

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