Two thoughts.

(1) The Windows shortcut for Firefox has the option to set "compatibility" settings. These can degrade the appearance of content in the browser. You can check those by right-clicking your Firefox icon (if Firefox is pinned, you right-click the pinned icon and then the Firefox icon two up from the bottom) and then Properties, and review the Compatibility tab. Nothing should be checked.

(2) In case your graphics card software was updated, could you try disabling graphics hardware acceleration?

You usually need to restart Firefox in order for this to take effect, so save all work first (e.g., mail you are composing, online documents you're editing, etc.).

orange Firefox button or classic Tools menu > Options > Advanced

On the "General" mini-tab, uncheck the box for "Use hardware acceleration when available"

If you restart Firefox, is the issue resolved or at least improved?

The Reset Firefox feature can fix many issues by restoring Firefox to its factory default state while saving your essential information. Note: This will cause you to lose any Extensions, Open websites, and some Preferences.

To Reset Firefox do the following:

1. Go to Firefox > Help > Troubleshooting Information.
2. Click the "Reset Firefox" button.
3. Firefox will close and reset. After Firefox is done, it will show a window with the information that is imported. Click Finish.
4. Firefox will open with all factory defaults applied.

Further information can be found in the Refresh Firefox - reset add-ons and settings article.

Did this fix your problems? Please report back to us!

Reset the page zoom on pages that cause problems.

• View > Zoom > Reset (Ctrl+0 (zero); Cmd+0 on Mac)

• http://kb.mozillazine.org/Zoom_text_of_web_pages

Also make sure that your ISP doesn't send the images compressed with a lower resolution to speed up the page loading.