I'm pasting my post from their support forum about the all white page back rounds and certain text that is normally in color but only black in 1.5. All of this, even though pages should load with the web sight colors. Heck, I couldn't even change the colors using the FF settings.
"I tried every suggestion offered on 11/29 and 11/30, some of which were: create new profile and edit about:config. I eventually bailed and reverted back to 1.07. This morning I tried again. First I installed 1.5 "over" 1.07, white pages. Then I did a complete uninstall, removing program files, %AppData% files and using three registry cleaners, white pages only. For the two installs this morning, I even turned off all security systems, thinking that might be part of the problem. During all attempts SpellBound and Adblock (only extensions I use) were not installed. I'm back using 1.07 and all web sites are rendering normally. If you had this problem and corrected it or found the cause please reply, because I want to be part of 1.5! Thank You!"

Remove AdBlock, see if you have the problem.

Use Adblock Plus if this resolves your issue.

I didn't have any extensions installed this morning during my two attempts to install 1.5. The other night when I discovered the problem, the first thing I did was to remove Adblock. The thing is, the first several days there were other threads about the same issue on their support forum, so I know I am not the only person that had this problem.