On Dec. 13th, 2012, I found a reproducible error at a site that seems to show at least a bug of Xfwm4.
The way to the bug:
I looked for a controlling device of a boiler at
with the expression "Siemens L & G RVP 211.1".
Then I followed the proposed link
to a site with a list of different controlling devices.
On Dec. 13th, I used the link of the device "RVP 211.1" (a bit below the top) and came to a site with a reproducible error ("Error 1").
On Dec. 14th, I recognized a slightly deviating error at the site with the list itself ("Error 2").
The top bar of the window frame the browser shows green horizontal stripes so it makes it difficult to read the text on it.
After some time, at least after enlarging (and reducing) the photo in the middle of the site by clicking on it, every text created by text fonts is destroyed.
I mean every text that is shown by the browser, by the window manager and by Leafpad. Only the "Document Viewer" (for PDFs) seems to be a exception, but this could depend on the type of file.
The top bar of the window frame of the browser and every other program is destroyed (without the colour green), including the symbols to enlarge or close etc. the window. (The functions are still there.) Every text created by text fonts is destroyed, too (like "Error 1").
After rebooting the computer, everything is okay, but the error is shown again at the same web site.
Acer TravelMate 290 (an old laptop computer)
with Linux 3.0.0-28-generic
(ClamAV did not find any virus.)
(I am not sure that a really use XFCE 4.8.3. Every version from 4.8.0 to 4.8.3 may be possible. Thunar is 1.2.3.)
Xfwm4 version 4.8.2
I checked the web site with "Parted Magic 2012_05_30", too. The sytem crashed (Firefox was "frozen", the CPU was at 100%). Parted Magic uses LXDE.
So the problem may show a general bug of Linux, too, but it is transported by Firefox und XFCE. Moreover, the "Error 2" is a problem of Xfwm4 with no doubt. It remains if Firefox has been closed.
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