The problem has been that certain fonts used by certain websites show up looking somewhat pixelated or granular-looking, unlike the smooth fonts other browsers will display for the same text. See the top headlines in the screenshot below to see what the problem looks like.
The problem seems to be that core X fonts are enabled in Linux Opera by default, and the solution is as easy as disabling them through opera:config#UserPrefs|EnableCoreXFonts (the "Save" button is at the very bottom of the page). Restart Opera, and you’re good to go.
Posted by Dynaflow