Hi fergus0n, This is a really nice computer. Please clear the cache for the site and please update your plugins for Flash and webGL.Upgrade your graphics drivers to use hardware acceleration and WebGL

A tall rectangle with two rows of two characters? This indicates that the page uses a character in a font that Firefox is not able to load and not able to substitute. In the case of Yahoo, they replaced icon images with a downloadable font. (This happened in the consumer interface many months ago.)

First, let pages choose their own fonts. That is set in the Options dialog here:

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

Make sure the box is checked for "Allow pages to choose their own fonts". (That's the default setting, but some users turn it off.)

If you reload the page (Ctrl+Shift+r will bypass cached files and pull everything fresh) and still don't get those characters, it's possible that font downloading is blocked somewhere else:

(1) If you use the NoScript extension: check for "Blocked Objects" on the menu that drops down from the NoScript toolbar button. You can switch an option in NoScript to allow web fonts for trusted sites. (See: Some Unicode characters are not displaying properly)

(2) Built-in global preference (the default value is true, but some users switch this to false). To check on this:

(a) In a new tab, type or paste about:config in the address bar and press Enter. Click the button promising to be careful.

(b) In the search box above the list, type or paste gfx and pause while the list is filtered

(c) If the gfx.downloadable_fonts.enabled preference is bolded and user set to false, double-click it to restore the default value of true.

Any luck?