Firefox 7 actually included a really big reduction in the amount of memory it uses. Depending on the sites you use, how many you have open at once, what kind of content they have and how much ram is available on your computer, 1 Gigabyte of ram may not be unusual (in any browser). My Firefox is using nearly 1 GB right now but I have 25 tabs open including things like Google Reader and Google News which are more like programs than static websites.

That said, it appears that you have a lot of plugins installed. Each of them uses some amount of ram (some much more than others). It could be that there is one in particular that is causing problem.

• Try the steps in Troubleshoot issues with plugins like Flash or Java to fix common Firefox problems to see if this is the case.
• I don't know what extensions you have installed but you might also want to try the steps in Troubleshoot extensions, themes and hardware acceleration issues to solve common Firefox problems to see if any of these are at fault.

I used the solution by AliceWyman in this thread.

https://support.mozilla.com/en-US/questions/713600#answer-8632

Disabling that dom.ipc.plugins released 500 MB of RAM straight away and my browsing speed also picked up.

I don't know why FF puts such performance degrading plugins in an updated version.

My FF 8.0 uses about 180 to 350 MB depending on no.of tabs open.

amkeew,
What those instructions do is make Flash (a plugin that's not part of Firefox) run in the normal Firefox process instead of separately. What that means is that now, when Flash crashes Firefox will also crash. This removes a feature we introduced about a year and a half ago that lets plugins run separately and not crash the whole browser when they crash. See, What is plugin-container