When I upgraded to Windows 10, I noticed text on thunderbird was blurry or fuzzy. I googled up the web and had a lot of hit on this subject. There are variety of fixes suggested like…
1) disable hardware acceralation
2) Go to TB option page and change the gfx.direct2d.disabled to true
3) Set Windows display scaling to 100%
While I believe those suggesions are all true, none of them solved my issue.
Further observation into TB’s screen showed the text start out showing clear then after few seconds, it becomes fuzzy. It feels like the text are melting in front of my eyes.
Then I found this article
The article was for AMD graphics driver. My graphic chip is Intel HD graphics 4600, but looking at the Intell HD graphics control panel, I have found the 3D setting where Conservative Morphological Anti-Aliasing is set to on. Setting this option to off immediately resolved the issue.
It appears, when my PC was upgraded to Windows 10, the device driver was also updated and it introduced this CMAA setting. This may be a good technology for gaming, but not for Document application.