Firefox is slow

Edit: Someone pointed out that this is kind of a known Firefox issue, that CPU usage typically stays 20-50% but periodically goes to 100-110% and there isn't a definitive solution yet. Well, I'll leave this thread here in case anyone wants to share war stories, or simply commiserate.

Hey, all.

Recently, Firefox has become very slow at some points. I've done nothing new to my computer other than updating Adobe Reader. Here's a description of the issue(s):

1. typing text in a field, like this post. I'll type a complete sentence, and (usually) maybe only see the first character before the cursor freezes and I see the pinwheel/beachball thing. I keep typing, and eventually the text catches up.

2. clicking on a tab/link/text field, or scrolling with my mouse wheel. I get the same -- an approximately 2-5 second pause, see the pinwheel/beachball, then the act is executed.

3. youtube videos frequently pause the visual element while the sound continues. After 2-5 seconds or so, the visual part catches up.

Below is a list of stuff I've looked at, but I don't know where else to go or what to do. Any help would be appreciated!


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I looked at another topic, where someone suggested looking at /Library/Internet Plug-Ins. There's nothing in that directory. /InputManagers only has a directory called "Smart Crash Reports".

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Mozilla's site suggested looking at Add-ons. Here's the list I have:
Default Plugin 2.0 (Gecko default plugin)
Flip4Mac Windows Media Plugin 2.3.4
IPhotoPhotocast 7.0
Java Embedding Plugin 0.9.7.2 MRJ Plugin version 1.0-JEP-0.9.7.2
Java Plug-In 2 for NPAPI Browsers 13.3.0
QuickTime Plug-in 7.6.3 7.6.3
RealPlayer Plugin.plugin 0.0.1d1
Shockwave Flash 10.1.102.64
Silverlight Plug-In 4.0.50401.0

I don't know what the Gecko is, but the rest sound like normal stuff I use.

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Extensions:
Adblock Plus 1.3.1
DownThemAll! 1.1.10
Multi Links 2.0.0.17

Nothing crazy there.

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Themes:
eLeKtRo DaNcE

Realizing I have a plug-in with ****tarded alternate caps is embarrassing and typing it gives me a headache, but I kind of like it and have been using it for maybe a year?

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Not sure what else info to provide, so here's other stuff that might be relevant:

iMac 8.1
6 GB RAM
Firefox 3.6.12
HDD: Used: 180 GB Available: 138 GB