For those of you that follow me on Twitter, you've probably seen some of my tweets regarding major performance problems I've seen with the install of FireFox 6.0. FireFox 6.0 was released a couple of weeks ago and is treated as a 'force feed' update for FireFox 5.0. I'm not sure what the deal is with this braindead versioning that Mozilla is doing with major version releases coming out, what now every other month? Seriously that's retarded especially given the limited number of new features these releases bring, and the upgrade pain for plug-ins that the major version release causes.

Anyway, after the FireFox updater bugged me long enough I finally gave in last week and updated to FireFox 6. Immediately after install I noticed terrible performance. Everything was running at a snail's pace with Web pages loading slowly and most content actually slowly 'painting' the page. A typical sign of content downloading slowly. However these are pages that should be mostly cached on my system and even repeated accesses ran just as slow. Just for a reality check I ran the same sites in Chrome (blazing fast) and IE (fast enough :-)) but FireFox - dog on a stick.

Why so slow Boss?

While complaining lots of people recommended to ditch FireFox - use Chrome, yada yada yada. Yeah, Chrome is fast and getting better but I have a number of plug-ins that I use in FF that I can't easily give up. So I suffered and started looking around more closely at what was happening.

The first thing I noticed when accessing pages was that I continually saw accesses to the Google CDN downloading jQuery and jQuery UI. UI especially is pretty heavy in size and currently I'm in a location with a fairly slow IP connection where large files are a bit of an issue. However, seeing the CDN urls pop up repeatedly raised a flag with me. That stuff should be caching and it looked like each and every hit was reloading these scripts and various images over and over again.

Fired up FireBug and sure enough I saw something like this on a repeated hit to my blog:

Those two highlights are jquery and the main CSS file for the site and both are being loaded fully and taking a while to load. However, since this page had been loaded before, these items should be cached and show 304 requests instead of the full HTTP requests returning 200 result codes.

In short it looked like FireFox was not caching ANY content at all and constantly reloading all page resources. No wonder things were running dog slow.

Once I realized what the problem was I took a look in the about:config settings and lo and behold a bunch of the cache settings were set to not cache:

In my case ALL the main cache flags were set to false for some reason that I can't figure out. 

It appears that after the FireFox 6 update these flags somehow mysteriously changed and performance took a nose dive. Switching the .enable flags back to true and resetting all the cache settings tote default reverted performance back to the way it's supposed to be: reasonably fast and snappy as soon as content is cached and accessed again  from cache.

I try not to muck with the about:config settings much (other than turning off the IPV6 option) but when there are problems access to these features can be really nice. However, I treat this as a last resort so it took me quite some time before I started looking through ALL the settings. This takes a while, not knowing what I was looking for exactly.

If Web load performance is slow it's a good idea to check the cache settings. I have no idea what hosed these settings for me - I certainly didn't explicitly set them in about:config and while in FireFox's Options dialog I didn't see any option that would affect global caching like this, so this remains a mystery to me.

Anyway, I hope that this is helpful to some, in case some of you end up running into a similar issue.