How to find out which Firefox tab is using most CPU or memory?

Question

There are times when the Firefox responds reluctantly. And it is not only when I have opened many tabs. But there are cases when I have opened as many as 20 tabs and Firefox is working fine and there are cases when I have opened just 5-6 tabs and Firefox behaves lazy.

So, I guess it do not depend on the number of tabs and there must be a specific tab which causes the problem. Isn't there a way to find that tab out and close only that instead of closing Firefox completely1? Is there an addon for that, or a script?

Answer 1

Opening the browser to about:memory can show per-tab memory usage.

Further reading

• Techzine article about memory usage.
• Firefox about pages.

Answer 2

For Firefox, I've made an addon which displays tab memory usage in the corresponding tab's title.

It provides user with tab related stats and memory usage...

https://addons.mozilla.org/firefox/addon/tab-data/

Features

• How many tabs are currently open
• How many tabs have been opened during this Firefox session
• How many tabs have been opened since the addon was installed
• Displays tab memory usage in title
• Preference to toggle tab memory usage on/off
• Preference to set interval between memory usage collection

Answer 3

The BarTab extension for Firefox (not available for the latest Firefox versions) might be useful for improving the situation:

BarTab can intercept when tabs are loaded in the background or restored after a browser restart and will only load the content when the tab is actually visited. It also allows you to free memory by unloading already loaded tabs, either manually or automatically.

Otherwise, you might switch temporarily to Google Chrome, where Shift + Esc displays the per-tab usage: