A website (like email or wiki) will load normally, and then immediately narrow to only take up the left half of the screen. Doesn't happen with all sites.
I first noticed this when I loaded Yahoo mail, since though my browser window was about 85% of the width of my screen, the page itself loaded normally and then immediately shrunk down as if my browser was narrower. The same thing happens with pages on http://en.wikipedia.org/, and some others. This support page is fine, however.
In addition, the pages that show this problem also have had their default font changed. It might look like Tahoma, I think, even though my preference configuration is Arial.
Todas as respostas (2)
Reset the page zoom on pages that cause problems: View > Zoom > Reset (Ctrl+0 (zero); Cmd+0 on Mac)
Thank you, cor-el, but that's something I already tried.
If anyone is interested in reading everything I've done so far, please click the "More system details" link to the right of my original post.