Here is a quick and dirty cure for Opera's insistence on using a thoroughly repulsive sans-serif font on some web pages under Linux.
The pages concerned all seem to have in common that they use declarations like "font-family: Arial, sans-serif" rather than just plain "font-family: sans-serif". Arial looks like arse anyway, so I had already deleted it from my system, but that didn't help this particular problem.
Setting all of Opera's font configuration options under "Preferences" which were related to sans-serif fonts to Bitstream Vera Sans did not work. Even though Arial did not exist on the system, Opera did not fall back to these preferences when it failed to find it, but instead used some other default which there was no obvious way even to discover, let alone to configure.
Using lsof to determine which font files Opera had open showed that some of them were for Nimbus Sans, which puzzled me as nowhere had I configured Opera to use that. Nevertheless, using GIMP to produce copies of the text on afflicted web pages in various fonts and sizes made it clear that this was the problem. For some reason, recent versions of Opera, unlike older versions, were deciding to use Nimbus to replace the absent Arial, and Nimbus is a fucking hideous font.
Solution: stop Opera looking for Arial in the first place. I edited the Opera binary and replaced all instances (there were only two) of "Arial" with "Cuntl", on the grounds that the chances of that matching anything were negligible.
Success! On starting Opera again the afflicted websites had ceased to use an arse font and were looking decent again, using Bitstream Vera Sans. Repeating the check with lsof as a further confirmation showed that indeed Opera was no longer opening the Nimbus Sans font files.
Since one of the websites concerned was Google, and another was the Lucy Pinder TV forum, which I run and therefore visit frequently, this problem had pissed me off greatly and it was very pleasant to be able to kill it at last.
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