There is a new unpatched memory corruption flaw in the latest version of Firefox.  What this means is that hackers could drop malware onto vulnerable systems.
Chances are this will be fixed sooner, rather than later – here is a little more about the story from The Register:
Security notification firm Secunia reports that the security bug (which it describes as extremely critical) stems from errors in handling JavaScript code. The flaw has been confirmed in the latest 3.5 version of Firefox, [...]

Want to know exactly how you are making use of the Firefox web browser?  Here are six of the best add-ons for Firefox that will give you every statistic you would ever want from your own day to day usage.  From cache, to download usage, and even easy cache status – we have something here for everybody to make use of.
Net Usage Item – Displays a progress bar of your Internet usage (grabbed from your ISP) on your Firefox [...]

Are you running short on room for your multiple tabs?  TooManyTabs is an add-on for Firefox that will give you the ability to store up to 50 tabs in multiple extra rows with a simple click.
In turn, with this extra organization, you have better visualization and prioritizing for the pages you are navigating through.  Here are a few more details from the TooManyTabs developer:
Instead of allowing idle tabs to waste your PC’s memory, you can now put your tabs [...]

This is a ‘bit of news that might have been missed by some. It looks like Firefox 3 continues to gain praise for having a significant reduction in the amount of memory it uses over Firefox 2.
Over at Ars Technica this is what they are saying:
During intensive browsing with approximately 50 tabs, I have found that Firefox 3 generally consumes less than half of the memory used by Firefox 2.0.0.12. Firefox 3 is also snappier and more responsive when [...]

Firefox 3 Beta 4 is ready for download. Well there was some confusion yesterday on if it was out or not, so I decided to hold off on this till today. Yet again, Mozilla continues to surprise and amaze with improvements to the core product. Two of the biggest updates I would say would be:

Speed:
Improvements to our JavaScript engine as well as profile guided optimizations have resulted in significant improvements. Compared to Firefox 2, web applications like [...]

Firefox 3 Beta 2 just rolled out and I have to say things just keep looking better and better. I mean, I’m not really all that disappointed with Firefox now but with what is being done there are tons of improvements on the way.
This recent release includes approximately 900 improvements over the previous beta, including fixes for stability, performance, memory usage, [...]

Firefox uses a lot of RAM. It is the number one complaint about this otherwise awesome web browser. So what can you do to solve this issue? Well there are a few rumored fixed out there in the wild.
Here is the nitty-gritty about:config solution to the problem:

Open up about:config by typing it into your Firefox address bar.
Right-click, go to new and then integer and name it this: browser.cache.memory.capacity
For the integer value, enter in 15000 [...]

Think you might want to go back one day to learn about the history of Mozilla and the Firefox browser? What if somebody like Ben or Asa becomes president one day? Then this stuff might be pretty interesting to look back upon. Ok, it is interesting now. No need to wait for a presidential run. The Mozilla Digital Memory Bank is doing it’s best to preserve as much of Mozilla’s history as it can.
Organized by [...]

Think Firefox is a little leaky? Well, put down that phone and leave your plumber alone. I have an extension for you that will help you figure out where your leaks are coming from. The Leak Monitor Firefox extension ops up an alert dialog to warn chrome and extension developers about one particular type of leak. It warns when chrome windows close but leave other code pointing at their JavaScript objects.
[Learn More About Leak Monitor!]

Can’t get enough of that memory tweaking and fixing for Firefox? Well I think I have one more resource that should help you get your fix. Firefox Tweaks, Extensions and Optimizations gives just about every memory and performance tweak I have ever read about. The best part about it all, is they are all in one place.
[More Firefox Tweaks, Extensions and Optimizations]