Web content is loading hidden

I'm not exactly sure how to describe quite the nature of the problem that I'm having. The source HTML files on the web server are loading in any browser except for firefox with an added tag argument class="hidden". This argument for the tags that these show on are not present in the source HTML on the web server.

For example, <p> from the source file shows up as <p class="hidden"> on chrome or opera. It shows as <p class=""> on firefox. If we change <p> to <p class=lead'> in the source HTML file, chrome still loads it, but adds it into the argument, showing <p class="lead hidden"> on inspect. It seems pretty well intent on making sure it loads hidden, but we don't know why. I can remove the hidden part from it in chrome's content inspector, and it will show, but even if I ctrl+shift+r in chrome, it doesn't load the proper code from the server, so these arbitrary bits of content are just hidden.

This is only happening from one location. All devices whose non-firefox browsers are having this issue are on the same network while this happens. Connections from other users seem to work properly. There doesn't seem to be anything I can find about anyone else having issues such as this and I'm hoping someone, here, can clarify what's happening here and how to rectify this bug.