From Mozilla help files;

Try disabling graphics hardware acceleration. Since this feature was added to Firefox, it has gradually improved, but there still are a few glitches.

Yes, when I disabled this function fonts back to the normal. But this a serious question because this option became enabled on default.

Yes, I found out about that myself and filed a bug report. Leave Hardware turned off. Not having it should not hurt.

1031347 – Firefox Full Installer Changes User Settings

But there are some open bug ticket for this issue? Is expected to be resolved?

You can try to create a new Boolean pref on the about:config page via the right-click context menu with the name layout.paint_rects_separately and set the value to true and leave hardware acceleration and Direct2D enabled.

• layout.paint_rects_separately = true

That way you still have the benefit from hardware acceleration, but may not suffer from rendering issues.

You can open the about:config page via the location/address bar. You can accept the warning and click "I'll be careful" to continue.

• http://kb.mozillazine.org/about:config

I tried this but don't work. I think Mozilla should consider having this option disabled by default.

I tested with Google Chrome and nothing like this happen.

It is possible that Firefox uses a different font (bolder version) when hardware acceleration is used.

You can right-click on a web page and select "Inspect Element" to open the Inspector (Firefox/Tools > Web Developer). You can check the font used for selected text in the Font tab in the right pane of the Inspector.

Really sorry for delay, but had some problems.

I see that this problem has not been solved yet. The firefox with when enabled hardware acceleration continues to "blur" the fonts.

Even in firefox TAB you can check this. Let me give an example: http://s16.postimg.org/9a2pwgm8l/firefoxblurfonts.png

The first example is with hardware acceleration enabled and second with disabled. You can see clearly the difference.

The top image is pushed over one letter. Is there something invisible there?

What you mean with invisible?

You can see other example:

Enable: http://s1.postimg.org/yp14ox54f/enable.png

Disable: http://s1.postimg.org/uer272pf3/disable.png

With Hardware acceleration ON fonts come blur.

From Mozilla help files;

Try disabling graphics hardware acceleration. Since this feature was added to Firefox, it has gradually improved, but there still are a few glitches.

You can try to disable OMTC and leave hardware acceleration in Firefox enabled.

• about:config page: layers.offmainthreadcomposition.enabled = false

You can open the about:config page via the location/address bar. You can accept the warning and click "I'll be careful" to continue.

• http://kb.mozillazine.org/about:config

Yes, disabling fix this problem. But I lost the advantages of this feature.

cor-el, thank you for the suggestion. But unfortunately don't resolve and put worst: http://s18.postimg.org/6nwe739u1/ayers_offmainthreadcomposition_enabled_false.png