Here's the screenshots. Firefox on left.

Most likely, those are not GIFs but custom font characters. A lot of sites are switching to using these fancy fonts, probably to save on download time.

The most common reason for this problem is if you set Firefox to use a standard set of fonts instead of letting websites choose their own fonts. You can review/modify that setting here:

"3-bar" menu button (or Tools menu) > Options > Content

Click the "Advanced" button, then make sure there is a checkbox for "Allow pages to choose their own fonts, instead of my selections above"

OK that and reload the page (Ctrl+r) to see whether it loads the custom font.

If it still doesn't appear: font downloads might be blocked, either by a setting or an add-on. More suggestions if needed.

If this inhibits readability: let's discuss zoom options.

Letting the pages choose their own font resolved it. Thanks.