System restore is not fixing this issue because system restore unfortunately "fixes" system files and issues, not applications. A system restore may have fixed this issue if it was IE since IE is much more integrated with the OS than add-on browsers like Firefox and Chrome
I'm a heavy user of IE and Chrome, but do use Firefox and it is installed on all my computers along with Chrome and of course the default IE. As such, I have not extensively worked out Firefox issues, mostly very minor ones. However, I can gladly try and offer some assistance.
I'll assume for now that you have updated Firefox to the latest version. That can be done by clicking Help from the FF menu bar and then clicking About. Once the About window is displayed, there is a "check for updates" button available on the About window. The latest release is 11 (only a few days ago I updated FF to 11 on this particular computer I am on currently) .
I'll guess the operating system is windows XP 32 bit or Windows 7 32 bit, as these are the most common OS platforms at this time. The OS version may not make a difference anyway but it's good to have the information for a clearer picture.
Open Firefox, click "Tools" from the main menu, and then choose "Options" from the drop-down menu.
In the dialog windows that opens, you will see several choices at the top. Select the "Advanced" icon, then click the "Network" tab. Click the button marked "Clear Now." This will clear your cache.
Here is a short flash video I made for you that shows the steps (click the link below or copy and paste the URL in your browser to view):
Close and then restart your browser.
Click "Tools" from the menu bar and select "Options" once again. This time, select the "Privacy" icon from the choices at the top of the dialog window.
Click the link labeled "Clear your recent history" and the link labeled "Remove individual cookies."
Here is another short flash video that shows the steps (click the link below or copy and paste the url into your browser to see the flash video):
Close and restart your browser again. With some luck, the pages are no longer scrambled.