This has bugged me for a while, but on many pages viewed with Firefox on Ubuntu (but not on Windows or OSX) any é (e with an acute accent) is replaced by a й (the Cyrillic Short I). There are probably other examples, but this is the one I encounter all the time.
Why is this, and is there anything I can do to get Firefox to display the characters properly?
A screenshot that should read résumé:
Here's an example of a page where this happens: http://www.theonion.com/articles/company-immediately-calls-job-applicant-upon-seein,31669/
Interestingly, the title displays fine. Looking at the page source the characters that display correctly are simply é while those that do not are written as é, &eacute or é (I think).
Check the character codification settings. Open the menu Edit | Preferences and select the tab Content. There click on the Advanced... button under Fonts and Colors (highlighted in the image, below).
The Typography window will open and there you can check/adjust the character codification. Or perhaps you would need to change any of the other settings, like default fonts or not allowing webpages to show their own fonts.
Another possibility is that the Firefox is using the wrong character encoding for those webpages. You can check what character encoding (if any) those sites use by right-clicking anywhere on the page and selecting "View page source".
You might also want to check the settings under the menu View | Character encoding to see if the encoding selected corresponds to the one set by the webpage (here, whatever is selected would probably be different for different webpages), and under Autodetect to see if autodetecting is deactivated.