Does it look better in safe/troubleshoot mode (hold Shift when launching TB)? If it does, disable hardware acceleration in Preferences/General, in normal mode.

Does it look better in safe/troubleshoot mode (hold Shift when launching TB)? If it does, disable hardware acceleration in Preferences/General, in normal mode.

1. Yes, troubleshot mode text is sharp again 2. HW accel. disabled - does not helps, still blurry

Launch again in safe mode, 'Reset toolbars & controls', 'Make changes & restart'. Still blurry in normal mode? Using any extensions or custom themes?

Launch again in safe mode, 'Reset toolbars & controls', 'Make changes & restart'. Still blurry in normal mode? Using any extensions or custom themes?

1. Did check both checkboxes, make changes & restart - still blurry 2. "Continue in Troubleshoot mode" - sharp

Win10x64, TB v91.1.2 x64

No add-ons using, TB vanilla.

Hard to say what else could be causing this; broken layout, add-ons and hardware acceleration are the most common factors that are affected by safe mode. According to the kb page, which may be down at the moment:

   Safe Mode temporarily affects the following: 

   All extensions are disabled. 
   The default theme is used, without a persona. 
   The Just-in-time (JIT) JavaScript compiler is disabled. 
   The userChrome.css and userContent.css files are ignored. 
   The default toolbar layout is used. 
   Hardware acceleration is disabled.

To be honest, the text in your picture looks normal to me. Perhaps make a new profile from Help/More Troubleshooting, about:profiles, add an account, and see if it's blurry in normal mode. The current profile is untouched.

Thanks for the help, i will try the fresh install since the upgrade broke my setup. Attaching comparison of both states, so you be able to notice a difference.

Update, did:

1. ofsite 91.1.2x64 download, and fresh install 2. thunderbird.exe -p, and then selected existent profile

Result: - Blurry, so assume some profile settings affects the UI, which happened after update to v91.

This is a BUG:

1. did another fresh install 2. created "Blog & feeds"

and same Blurry text,

HW accel disable does not fix issues.

Fresh installs of the program are usually not effective. What is the result with a new profile? If it's still blurry in a new profile, you can submit a bug report (and cite this topic).

Fresh installs of the program are usually not effective. What is the result with a new profile? If it's still blurry in a new profile, you can submit a bug report (and cite this topic).

"Not effective", do you meant not affected ? I did exactly fresh install with clean data to see that the issue caused not by my profile/settings.

Yes, blurry after install, and it's ok, you can submit bug report, i did full description/report here.

Looking TB replacement now, really dissapointed with FF and TB.

I've located a bug report which is specifically about blurry text. https://bugzilla.mozilla.org/show_bug.cgi?id=1689845

Please check the following:

Menu app icon > Preferences > General scroll to the very bottom and click on 'Config Editor' Accept the risk in top search type: webrender.force look for this line: gfx.webrender.force-disabled If it says 'False': click on the far right toggle icon OR double click on line to toggle Value to 'True' REstart Thunderbird.

After reading the info in the bug report, someone using beta versions makes a note that after an update they had to disable another webrender preference after the one I mention had been removed.

There is also another option which needs exploring. preference 'gfx.webrender.software' is set to 'false' by default. Does setting this to 'True' help the situation - remember to restart Thunderbird and then report back on results.

Your input and feedback is valuable with helping to gain information about this bug report.

I've located a bug report which is specifically about blurry text. https://bugzilla.mozilla.org/show_bug.cgi?id=1689845 ...

gfx.webrender.force-disabled = true Sharp font as it should gfx.webrender.software Does not affect

Did every combination with restart after each change.

Thanks for the help.

I've located a bug report which is specifically about blurry text. https://bugzilla.mozilla.org/show_bug.cgi?id=1689845 ...

gfx.webrender.force-disabled = true worked for me. Thousand thanks! You've made my day. Sharp and clear fonts are back!