Messages do not display correctly

I have Pandora 5.6 installed on both a desktop computer and on a Dell Inspiron laptop. Emails that come in from individuals work correctly; they cover the whole screen and change size with the ctrl +/- keys. However, messages from other sources - health care providers, financial organizations, charities, stores, etc. -  do not display correctly. On the desktop, incoming messages display large enough to read but the Ctrl +/- keys to change size generally adds spaces in the message but has no effect on the message size. On the laptop the messages appear in a narrow column too small to read. The message size also does not respond to ctrl +/- keys. This makes Pandora almost useless on the laptop. I've fiddled with Settings for display and font options, read the Help file, gone through menus to no effect. I also have Thunderbird installed on both computers and messages work perfectly right out of the box with no setting changes. In fact Pandora is the only program that has display problems on my computers. Since others apparently do not have this problem, there must be something set wrong on both my computers. What do I have to do to fix this? Thanks.

Try with Ctrl+Shift +/- keys. That's optical zoom, better suited for bulk HTML messages.

Text size change (Ctrl +/- keys) will not affect HTML segments where font-sizes are specified explicitly.

Amazing what a difference one little key can make. Thanks!