Update!
I've experiencing strange web browsing issues that I think are related to the Avast UI issue I've been trying to solve here.
While on one of my threads over at TSF (Tech Support Forums), I noticed a strange glitch. Some elements on the page weren't displaying properly. Certain containers (divs, tables, etc) were stretched hundreds of thousands of pixels wide (seriously. I used Firebug to get the widths of elements). This gave me a tiny little horizontal scrollbar at the bottom of my browser. Most of the text in affected areas was just gone, however, in some cases, I could still see underline formatted (such as a blue underline for links and red squiggly underlines for spelling errors), even though there were no words there. I could select the invisible text, but all I could see was the highlighting. The next was never visible.
In addition to the stretching of the elements that forced the whole page to widen to the right, certain elements with borders had the borders shifted to the LEFT (just the borders, not the elements themselves).
At first, this only happened on one page of that specific thread on TSF. Then it happened with a specific message within a specific conversation within Gmail. I also noticed it again on another site but I don't remember what it was. When I returned to TSF, I noticed that it was not consistent there and would usually occur, but not always, and it would occur on any of the 3 pages of that particular thread.
Why do I think it's related? The last time this glitch happened to me on a website, it left a few letters of text here and there visible, and instantly reminded me of the Avast UI problem. I began to think... if Avast uses a restricted web-browser-like interface for displaying the content in its windows, it could explain why I'm getting the same effect. Explainable differences would include the stretching of elements. Without the presence of scrollbars in the avast UI, stretched elements wouldn't be noticed at all.
I realize this problem is now not something that belongs in the avast forum. It is a deeper issue. Still, if any of you have any suggestions, please do share. Oh yeah, and while I use Firefox as my browser, I tested this in IE as well as Firefox Safe Mode and it still happens, so that rules out FF addons.