Firefox issue: Poor font rendering or lack of loading in HTML5 reader

There is a known issue with the Mozilla Firefox web browser that prevents the ReadCube HTML5 Web Reader from loading on some computers. In particular, Windows and Linux systems are known to be affected.  If Firefox is not able to correctly recognize your graphics card for enabling hardware acceleration, a feature called DirectWrite is disabled. This in turn can affect font rendering. We want to ensure an optimal reading experience with the ReadCube Web Reader and therefore do not load in Firefox browsers with this disabled graphics state. 

This is a known issue with Firefox and is not specific for the ReadCube Web Reader. Please see:


It is possible to manually enable DirectWrite in Firefox. We provide the directions below but please note, this does not guarantee optimal font display and may affect browser speed. To manually enable DirectWrite font rendering in Firefox:

1) In the address bar, type “about:config” and press Enter
2) Search for the preference name: “gfx.font_rendering.directwrite.enabled” 
3) Double-click on it, and set the value to “true”
4) Restart Firefox and check the web reader

5) If the problem persists, please repeat the above for: "gfx.font_rendering.directwrite.force-enabled"
6) Double-click on it, and also set this value to "true"
7) Restart Firefox again and check the web reader

If the above steps do not address the issue, unfortunately the only remaining advice is to please try another web browser (such as Chrome, Internet Explorer, Safari or Opera). You can also reach our customer support at support@readcube.com. Since this is a general known issue with Firefox, please direct any specific requests for information about the browser’s hardware acceleration/DirectWrite settings to Mozilla Firefox support.

Feedback and Knowledge Base