As you can see from your screenshot, Firefox is using 768.6 MB of RAM, which is 37.5 % of your available RAM. That is due to lots of tabs, as you mentioned in your original post.
Depending on what MacBook you have, you can get 4 GB (two 2 GB modules) for less than 30 USD or can get 8 GB (two 4 GB modules) for less than 50 USD.
You might also just get one 4 GB module and have 5 GB RAM, as many older MacBooks can support 6 GB of RAM.
To find out, what exact Mac model you use, click
> About This Mac > More Info > Hardware Overview:
To see a more elaborate image explaining the above steps, click
here.
To see a more detailed video tutorial showing the above steps, click
here (2 MB, 23s, .mp4).
For images wider than 800 pixel, please use the TIMG tags instead of the IMG tags by just adding a T in front of the [url= and closing ]Image[/url] tag, like [img] and [/img] to prevent horizontal scrolling.
You can use the
Image to edit your images and add the Ts.