First, I would like it to be noted that this bug does not exist in Linux, particularly on Ubuntu 9.04-Jaunty Jackalope (as discussed with AY -see comments at sidebar). This bug appear to affect Windows Operating Systems only (Vista and XP, don’t know if the older Windows OSs also have this issue). The tests I have made on my Ubuntu proves that its not affected with this bug. Start-up speed was fast, amazingly faster than on my Vista box.
Workarounds, temporary fixes are currently circulated online (here, here and here), just to ease this problem a bit.
The bug has already been reported and tracked at bugzilla.mozilla.com with Bug 501605 as code (see here). Patch is already underway posted on the same bug report (see comment 131 at bugzilla), where there is also a try-out version of the software containing the patch — this patch is deemed to produce Firefox 3.5.1. If you are bold and daring enough, you may download the Firefox v3.5.1Pre from the download links page of this blog. Be sure to back up your profile, just to make sure everything is safe.
My experience with Firefox 3.5.1Pre? After downloading the zip file and extracting, I removed my Firefox v3.0.11 on my Vista. The download seems to be a portable version, you just extract and click firefox.exe and you’re up and running. My early observation is — it’s fast. The lag seems to have been fixed. I also have noticed that this try-out version is codenamed: Shiretoko. Sounds good for a patched try-out version that also works good. As I have said, if you are brave enough, try it out and see the difference. I think you’ll like it.
Additionally, let me post a quote from blurnot.blogspot.com saying,
A quick google will reveal you are not alone, Mozilla has acknowledged the flaw and hoping that their developer will be able to fix it. Ambiguity is not something that the end-users are looking forward to hearing. With the launch of Internet Explorer 8 and newer versions of the Chrome, Mozilla has got to fix its slow startup speed in Firefox 3.5 lest they lose their lead in the browser war.
I really hope that people won’t ditch Firefox 3.5 only for this problem. If this problem is wrecking your nerves, reverting back to Firefox 3.0.11 would be a welcome, short-term, bail-out solution (link added at download links page).
Stay tuned for more updates.