...or at least two specific toolbars.
For the longest time, I could not figure out why the heck Firefox refused to respond to mouse-clicks until 10 seconds after I opened the window, even if I already had one window of Firefox open.
Then, today, I noticed that I was getting lag.... yes..... LAG.... the CPU/GPU type of lag... when trying to type into a text box of all things. A Text box.
Here I am, sitting on a computer with 8GB of RAM that can play several games at max settings, and it is being bogged down by friggin Firefox while typing in a Text Box.
I did a Ctrl+Alt+Del, opened Task Manager, and... woah.
Firefox was using 160 Megabytes of RAM? What the heck!? Also, it was using up 30% of my CPU resources. Thirty freaking percent of CPU resources on a _gaming_ machine.
Here, it turns out that Toolbars were the culprit.
I had these toolbars installed:
AVG
Daemon Tools
AIM
Plus what normally comes with Firefox. I had them hidden, but installed. As soon as I showed them, WHAM, lag gone, now Firefox is only using up about 40-70MB.
But I never even _use_ these toolbars... so I went into Addons and clicked "Disable" on Daemon Tools and AIM.
BOOM.
Problem Solved. No more Lag, and Firefox responds to my Mouse-Clicks as soon as it loads up. It appears the AIM Toolbar was causing the initial unresponsiveness, and Daemon Tools was the cause of the ridiculous RAM usage.
So, if any of you ever run into a problem like this with your Firefox, consider disabling toolbars you don't need/use. Hiding them is not enough -- they will continue to run in the background, they need to be disabled through the Addons window.
Edit: All of the above applies to Windows7 64-bit. Dunno if the 32 or any of the WindowsXP versions do it.