I saw a great tip today: by adding a simple preference in your Firefox configuration, you can tell Firefox to reduce its memory usage to 10 megabytes every time you minimize the application! This has worked very well for me - here's how you do it:

In the Firefox address bar, type about:config and press Enter.
Right-click in the page and select New -> Boolean.
A pop-up box will appear. Type config.trim_on_minimize and click OK.
Select True and click OK.
It will take effect the next time you startup Firefox. You can check it out by opening your task manager (right-click on the Windows taskbar and choose Task Manager) and watching Firefox's memory usage as you minimize and maximize the application.

or second way


In the Firefox address bar, type about:config and press Enter.

Scroll down and find the entry that says dom.max_script_run_time
Double-click on that entry and change the value (the default is 5) to something higher. Most sites recommend 20, but I found that I still received the pop-up warning too often. So I changed it to 1000!
Click OK.
Restart Firefox

The script timeout in Firefox can be increased to avoid the "Warning: Unresponsive script" popups.



In the URL bar, put about:config. Then, look for dom.max_script_run_time under "Preference Name". Right-click the name and click Modify. Set the value to something higher than 5, such as 30, then click OK.