Previously I reported that Mozilla Firefox has been really unstable lately. Quite often, when closed firefox it would stop responding. More often than not, when I launched firefox it would warn me that the previous session had been interrupted when in fact it had managed to shut down normally. The problem had become so annoying that Internet Explorer was actually more more usable.
The firefox situation has been a constant source of consternation. I had not installed any new applications recently and all virus/spyware scans reported that my system was clean. I haven’t installed any new Mozilla add-ons or themes. I was ready to give up and just use Internet Explorer on my notebook (this problem has not manifested itself on my desktop).
Today I finally discovered the source of the problem, DEP! Data Execution Prevention was killing the Firefox process at shutdown. DEP is enabled in Windows Vista by default for essential windows programs and services only: however, I had enabled it for all programs and services. I can only speculate that either firefox has a memory leak that is setting off DEP, or a normal part of Firefox shutdown is causing the exception.
Anyway, adding the Firefox executable to the allowed list in the DEP control panel seems to have settled my flaky Firefox Fiasco.
From Microsoft Help and Support:
Data Execution Prevention (DEP) is a set of hardware and software technologies that perform additional checks on memory to help prevent malicious code from running on a system … The primary benefit of DEP is to help prevent code execution from data pages … Software-enforced DEP can help prevent malicious code from taking advantage of exception-handling mechanisms in Windows.
A detailed description of the Data Execution Prevention (DEP) feature in Windows.