I am accessing the PDF from this site: http://www.fourierandwavelets.org/

This is the URL for the PDF: http://www.fourierandwavelets.org/FSP_v1.1_2014.pdf

When I look at the preferences->applications in Firefox, PDF is set to Preview in Firefox. Apparently the previewer is part of Firefox, and not Okular, which is what Konqueror is obviously using. Is there a way to change this behavior? Are others seeing the same thing? I know (or believe) Acrobat is no longer maintained for Linux.

This is what it looks like in Firefox. Note the summation range is place on the base of the sigma, not under it, where it belongs.

In Konqueror it looks like this. Note that the mathematical symbols are properly placed.