
After upgrading to Firefox 4.0 some PDF usually visualised inside firefox are not visualised (seems random).
After the upgrade to Firefox 4 (in Debian Linux for AMD64) the PDF files open inside firefox with the Acrobat Reader plug-in are not always visualised. After initiating Firefox usually they appear, but after opening a number of them the window just keeps white and nothing happens. Example of these PDFs are the ones that can be found in IEEExplore, ScienceDirect, and so on. I have updated the Acrobat Reader to the last release and it happens the same.
The operating system is Debian 5.0 compiled for x86-64, but Firefox and Acrobat Reader are the 32 bit versions.