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I have been having this problem with accessing PDF documents in Firefox for as long as I can remember, up to a point that I dread clicking on any PDF document when searching on Google. Well, the problem has reached the critical annoyance threshold, and as I have a bit of time this fine sunny afternoon, I have decided to tackle it once and for all.

The problem is as follows, once I click on a link which invokes the Adobe Acrobat plugin in Firefox, the document is loaded in embedded mode into the browser itself. Everything is fine at this point. However, if I click on the "Close" or "Back" button on the browser, the browser window just gets blanked out, and the Task Manager indicates that my Firefox session has maxed out the CPU (up to 90-99%). This goes on for a good 20 seconds before the system recovers and Firefox is back to normal. Usually, at this point, I use the Task manager to kill Firefox, but it is so annoying that you lose your session and have to restart all over again. I tried this in Internet Explorer and it does not suffer from this problem at all. All these problems are observed on Windows XP SP2.

Searching on Google tells me lots of other people have the same problem, although none of the online forums seem to offer the solution. Some people point the finger at Firefox, others at Adobe (maker of Acrobat), and visitors from other planets favour a conspiracy theory by the US government and Mircrosoft.Uh huh !

The first thing is to fire up the File Monitor and Registry Monitor utlities to see what these processes are up to. You can download these excellent applications from the Sysinternals website (the folks who discovered the Sony XCP Rootkit, remember ?). These applications will capture all accesses to the file system and the registry, although you will need to specify a filter so that only activities related to Firefox and Adobe Acrobat are displayed, or you will be overwhelmed by the amount of junk spilled out into the capture log. There is a filter popup, in which I typed "AcroRd32.exe;firefox.exe" into the "Include:" field, which represent the two executables of interest. I then went through the same ritual of opening the PDF inside Firefox, then closed it, and watched the output of the Monitors. The Registry Monitor showed nothing of interest, however, the File Monitor showed clearly that at the point of the 100% CPU being observed, Acrobat was trying to access the File:

C:\Documents And Settings\David\Application Data\AdobeUM\WWW_OpenURL

Which promptly returned "NOT FOUND". This went on for about five times before Acrobat started accessing other files and carried on, which was also when my Firefox session went back to normal. This does not look like a coincidence. I checked the above path and there is already an empty directory at C:\Document And Settings\David\Application Data\AdobeUM, but it is just an empty directory. A bit of Google search shows that the AdobeUM directory is used by the Adobe Update Manager to contact the mothership for any newly spawned Acrobat mutants, and it looks like my Galactic firewall is preventing it from doing so somehow. Very interesting. I fired up Acrobat in stand alone mode to check on the Auto Update mode, and sure enough, I already disabled automatic update. So the question is, why is it insisting on contacting mummy ?

To add to the mystery, I tried this same thing under Internet Explorer, the "NOT FOUND" message was also displayed in the File Monitor, but only once, instead of five times as in Firefox. So the problem exists in IE too, although much less noticeable.

Who knows, maybe there is a hidden can of worms somewhere here, but for me and my immediate earthly needs, I promptly created an empty WWW_OpenURL directory in the AdobeUM directory, and hey voila! mes amis, the problem disappears in puff of smoke. Firefox now returns to the previous page in lightning fast speed once I dismiss a PDF document from the Acrobat plugin.

For your information, I have Acrobat 6 and Firefox 1.0.x, although it seems this problem has been experienced by people using Acrobat 7, and Firefox versions up to 1.5.x. As the problem is centred around the Update Manager, you should also make sure:

•  your firewall allows the Adobe Update Manager through
• Acrobat is configured correctly for browser embedded mode. It might help to re-install Acrobat if you apply all the suggestions here and it still does not work

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