The "hanging/freezing/not responding" problem that existed in all versions of Firefox 3.6 persists in Firefox 4.0

Question

Starting on April 14, 2011, I tried installing Firefox 4.0, which I downloaded from the Mozilla site. The first couple of times I tried to install it, it corrupted Firefox file places.sqlite. I know this because the install renamed the file to places.sqlite.corrupt. Luckily, I had recent backups. My previous installed versions were 3.5.18, which I had been using up to this time, and 3.6.16. I tried installing 4.0 with 3.6.16 installed, which I installed only for the sake of installing 4.0, and with no previous version installed and got the same bad results. I finally got a "successful" install on April 16, 2011, with no previous version installed.
Early on I discovered that Firefox 4.0 hangs (Firefox not responding) when left to idle for exactly 5 minutes (I timed it several times after immediately starting Firefox), pegging a constant 50% of the CPU when it hangs. I left it in a hanging state for up to half an hour, but nothing changed. This problem existed for all versions of Firefox 3.6, which is why I didn't install version 3.6.16 until I was ready to install version 4.0. I never kept any version of Firefox 3.6 installed for more than a couple of hours because of this problem. I need to be able to let Firefox stay idle for long periods of time -- certainly for more than 4 minutes and 59 seconds -- without having it hang, and I was able to do that with all versions of Firefox prior to version 3.6. It's incomprehensible that Firefox 4.0 has to always hang if it's inactive for more than 4 minutes and 59 seconds, and it's incomprehensible that this problem has been present and persistent since version 3.6 was introduced. To believe that 4 minutes and 59 seconds is sufficient idle time for a browser is absurd. This was never an issue with any version of Firefox prior to version 3.6, this was never an issue with Netscape, and it's not an issue with IE 8.
There are 2 other problems related to the hanging problem. If the browser and the bookmarks library are both open and the browser is closed normally, the bookmarks library remains open. After being left idle for exactly 5 minutes, the bookmarks library hangs, pegging a constant 50% of the CPU. If Firefox 4.0 is restarted before the 5 minute idle limit, it starts successfully. If an attempt is made to restart it after the 5 minute idle limit, it won't start. If the bookmarks library is left open for less than 5 minutes after the browser is closed, it can be closed successfully. In all versions of Firefox prior to version 3.6, the bookmarks library automatically closed when the browser was closed. The other related problem is that Firefox 4.0 occasionally pegs a constant 50% of the CPU without hanging even while it is being used and even if the only thing open is the home page, which in my case is google.com. Firefox can be used while this is happening, but it is worrisome and shouldn't be happening. Normally, Firefox 4.0 uses no CPU when it is left to idle within the 5 minute idle limit.
Firefox 4.0 has not crashed on its own yet, so I've had no crash reports to send to Mozilla, but because I've had to use the "End Now" button on the Microsoft unresponsive program window numerous times to terminate it when it hangs, numerous Microsoft Windows dump reports have been generated, all of which I've sent to Microsoft.
The last fully working version of Firefox I had was 3.5.18. Unfortunately, I don't have the installer for that version and Mozilla doesn't make it available anymore. Also, it looks like version 4.0 altered the places.sqlite file such that I might not be able to go back to version 3.5.18 even if I could. If I could reinstall version 3.5.18 and get it to work with the altered places.sqlite file, I would, but it is outdated and no longer supported by Mozilla, and I only want to use up-to-date and supported software.
The hanging problem is totally intolerable and unacceptable. If I can't get a version of Firefox 4.0 anytime soon that doesn't hang after being idle for just 5 minutes (why 5 minutes???) or for any limited amount of time, I'll have to install and use Google Chrome as a permanent replacement for Firefox. (If I do have to replace Firefox with Google Chrome, how can I get my Mozilla Thunderbird e-mail links to open in Google Chrome when I click on them?) Based on other user feedback regarding this problem dating back to the very first Firefox 3.6 version, Mozilla has had ample time to resolve it. I have found other problems with Firefox 4.0, but I'm not going to bother telling Mozilla about them because if the hanging problem isn't resolved soon, I'll have to stop using Firefox permanently. I can't and won't tolerate the hanging problem. I have been using Firefox exclusively for many years, but my disappointment with it has been growing since version 3.6 was introduced and my patience has run out.
I would appreciate Mozilla letting me know within a week of this posting if they can't or won't fix the Firefox 4.0 hanging problem. If I don't receive a substantive response to this problem within a week, I'm going to have to abandon Firefox permanently and switch to Google Chrome. I'm also going to leave a negative review of Firefox 4.0 on CNET to warn other potential users of the hanging problem.
I am running Windows XP Media Center Edition 32-bit SP3 on a Dell XPS 400 desktop computer. I have an Intel Pentium D CPU 2.80GHz, 3.0GB Dual-Channel DDR2 RAM @ 265MHz, RADEON X300 SE 128MB HyperMemory, and 190GB of free space on my hard drive. I am using COMODO as my firewall and Avira AntiVir as my anti-virus software. I am also using WinPatrol and Secunia PSI. My ISP is AT&T. My download speed averages 2.5 Mbps, and my upload speed averages 0.65 Mbps. All of my software is up to date, thanks to Secunia PSI and CNET TechTracker, and my computer is free from infection.

Answer 1

Another aspect of the Firefox 4.0 "hanging/freezing/not responding" problem has emerged. I have found that on the common occurrence when Firefox 4.0 occasionally pegs a constant 50% of the CPU while idling within the 5 minute idle limit and I close it normally, it disappears from the Task Bar but continues to run and continues to peg a constant 50% of the CPU. I tried restarting Firefox 4.0 and got the following message: "Firefox is already running, but is not responding. To open a new window, you must first close the existing Firefox process, or restart your system." Before Firefox can be restarted, the existing Firefox process must be killed via the Task Manager or Process Explorer (I use the latter), after which a Microsoft Windows dump report is immediately generated. I always allow the dump to be sent to Microsoft.
The three big questions that have gone unanswered by Mozilla are 1) why did the hanging problem start with the very first release of Firefox 3.6, 2) why was the problem allowed to continue on up to and through Firefox 4.0, and 3) why hasn't Mozilla fixed the problem yet? And what is the significance of the 5 minute idle limit? Do Firefox 3.6 through 4.0 try to launch something when the browser and/or the bookmarks library have been idle for exactly 5 minutes? Maybe it's a problem with the number and/or type of plugins and extensions and/or the number of bookmarks. Maybe Firefox 3.6 through 4.0 work just fine if there are few to no plugins, extensions, and bookmarks, but that doesn't realistically accommodate users. Whatever the cause of the problem, Mozilla should have had a handle on it by now.
If anyone from Mozilla Support is reading this post, please let me know if it is possible to roll back Firefox 4.0 to Firefox 3.5.18. If it is possible, how do I do it, and where can I get the installer for Firefox 3.5.18? If I can reinstall it, I'll use it until Secunia Software Inspector informs me that it is insecure and no longer safe to use. At that point (maybe much sooner), I'll switch to Google Chrome exclusively because I don't want to use outdated software that is insecure and because I don't believe that Mozilla intends to fix the hanging problem and is willing to lose users over it. I certainly don't want to use software like Firefox 4.0 that has such an impactful problem. If I do have to abandon Firefox, how can I click on Mozilla Thunderbird e-mail links and get them to open in Google Chrome?