I have the exact same problem I have no idea what the deal is. I've tried everything myself. Must just be a bug with the new versions I don't know. They will hopefully fix it or someones needs to tell me how to.

This issue can be caused by the bitmap version of the Helvetica or Geneva font or another (bitmap) font that can't be displayed by Firefox in that font size. Firefox can't display that font in the specified size and displays gibberish instead. You can test that by zooming out (View > Zoom > Zoom Out, Ctrl -) to make the text smaller.

Uninstall (remove) all variants of that not working font to make Firefox use another font or find a True type version of that font that doesn't have the problem.

See also http://kb.mozillazine.org/Issues_related_to_fonts#Gibberish

No offense to Mozilla, who have developed a fine product, but it's a bit insane that those of us who use Helvetica should have to delete it for this product to function. None of the other browsers have that issue, so it couldn't possibly be that difficult to correct. This is a major problem for anyone who does any graphic design. We shouldn't have to choose between functionality and our work.

I agree with wholeheartedly with twrex. Please fix it.

It is caused by using old Mac versions of the Helvetica font. If you only have modern vector type (Open Type, True Type) versions of Helvetica installed then there shouldn't be a problem.

You can try to increase the value of this pref: browser.display.auto_quality_min_font_size (20)

Why would a Windows computer have old Mac fonts installed?

I have the same problem on Windows XP SP3. I've updated Firefox twice since I switched from Internet Explorer 7 and am now using version 3.6.12 and still have the problem. In my case, what I assume are "special symbols" display as an outline rectangle with 2 rows of 2 numbers inside the rectangle. I've used other answers within the support forum to change font size, change the character encoding, not allow the web page to use its own font, etc. So far, those things have not helped.

You seem to be using Unicode (UTF-8) to show that text.

You can try some different Western or Windows encodings or Auto-Detect : Universal to see if that helps.

View > Character Encoding

Making the suggested changes altered what I see, as shown in the attachement, but I still have a problem.

You need to use UTF-8 to display that page and not a Western encoding. Choosing Universal may not detect the encoding correctly in all cases, so you may need to try different encodings on some site if the server doesn't send the correct encoding. It can even make things worse and in such a case Auto-Detect is off is the recommended setting.

What is the default encoding (used when the server doesn't specify one) ?

Tools > Options > Content : Fonts & Colors: Advanced > Default Character Encoding

I was using UTF-8 before and changed it after reading your previous suggestion. The attached will show the settings you questioned.

The page /questions/670622 (How do I get rid of these strange characters) in your above search results image doesn't display well for me. So that is a bad example and you can't get that page display correctly. That (”= %e2%80%9d : ”) looks like that text was copied as Unicode and send as Western encoding by the server and that corrupted the characters.