I am using Kubuntu 12.04 and tested this in a fresh user account. After entering every subcategory in the Systemsettings for Application Appearance (on my german system "Erscheinungsbild von Anwendungen") the font appearance in Firefox and Thunderbird changes (the antialialising looks really bad). I did not klick on the "Apply" ("Anwenden") button. Just opened Systemsettings > Application Appearance and klicked "Colors", "Symbols", "Fonts", "GTK+ Appearance", "Emoticons" one after each other. After that I restarted Firefox and Thunderbird and now the fonts are looking ugly even after a reboot. Reproducible: Always Steps to Reproduce: GUI Names could be wrong because I translated them back from the german names. 1. Create a new user 2. Login to KDE as the new user 3. Start firefox 4. Make a Screenshot of e.g. the top black menu bar on google pages 5. Open "Systemsettings" 6. Select "Application Appearance" 7. Select "Colors", "Symbols", "Fonts", "GTK+ Appearance", "Emoticons" 8. Close the "Systemsettings" window 9. Restart Firefox 10. Make the same screenshot in Firefox and compare it to the one made in step 4. Actual Results: The font's appearance of the first and the second screenshot differs (the second looks somehow dirty). Expected Results: The font's appearance should not have changed because I changed no setting.
It is not only the appearance of the font on the websites that have changed but also the font's appearance in the tab-text or firefox's menu (see attached screenshots).
Created attachment 70522 [details] Screenshot taken in Step 4
Created attachment 70523 [details] Screenshot taken in Step 10
Created attachment 70527 [details] .fonts.conf as it is created by the systemsettings > application appearance > fonts dialogue
I tracked it down to the file ~/.fonts.conf it is created when one enters the "Fonts" settings (in "Systemsettings" > "Application Appearance"), see attachment. If I change the following const value <edit mode="assign" name="rgba"> <const>none</const> </edit> from "none" to "rgb" and additional the following const value <edit mode="assign" name="hintstyle"> <const>hintmedium</const> </edit> form "hintmedium" to "hintlight", than the fonts are looking much like the default settings (without the .fonts.conf file). So the Bugfix should ensure that a .fonts.conf file is created, matching the default settings.
*** This bug has been marked as a duplicate of bug 245664 ***