RSS feed glitch with Firefox and Safari browsers

I’ve been using a hack to correct an issue and would like to know if there is a different way to resolve it.

I have found on both MU and non-MU installations of WordPress that RSS feeds are cut off abruptly with a […] when viewed in Firefox or Safari. This is a frustration for RSS subscribers who prefer to read the entire article in their feed readers, rather than click through to the blog. It is also a serious problem for our branded iPhone application, which pulls in headlines via the RSS from WordPress.

I have checked the options and the settings are set to show full text.

The hack that I have been using is outlined here: https://devilsworkshop.org/force-firefox-to-display-your-full-feeds-wordpress-hack/

The sites where this has been a problem are:
https://blogs.ivey.ca
https://www.melissacheater.com
https://www.pseweb.ca
and a few others for various clients.

Thanks so much for any feedback!