Last day i was going through some articles in net and reached a weblog in which there are some solutions for this issue.
According to Justin(am taking the main points and adding the comments and my opinion) The things that you can do when you feel like your system is crawling while using firefox are.
1. Check the pages you are viewing
Whether the page contains flash, larger amount of data, animations, movie etc... ( big page big usage)
2. Restart the Application
Yeah, This is a sure shot way, when I was working with an ISp support, and when we were stuck at one point of time, the sure shot way to kill time and explore reason(why the customer is not able to connect) was to restart the computer. :) clear the cache and temp files as well.
3. Kill the plugins and themes.
Yeah, if you have the themes and plugins that are useless, then kill them. The basic, standard theme is the best to look at.
4. Memory leaks and usages
about:cache?device=memoryin any of the windows and find what all objects are eating your resources. (phew! when I tried that, I was convinced that I should use the browser in a text only mode, I should at least disable images, yeah, images were taking toll in my browser, Did i mentioned that I've 8+ windows opened?) Memory leak detection can be done by referring a post of Jesse Ruderman.
You can also modify about:config
* Addition: Let the browser(and computer) be updated, no no to beta versions please...
Source: Un edited post in Justin Shattuck's blog