Start Firefox in Safe Mode {web Link} by holding down the <Shift>
(Mac=Options) key, and then starting Firefox. Is the problem still there?

FredMcD said

Start Firefox in Safe Mode {web Link} by holding down the <Shift>
(Mac=Options) key, and then starting Firefox. Is the problem still there?

Yes.

Interesting.

Start your Computer in safe mode with networking. Then start Firefox. Try Safe websites. Is the problem still there?

Starting The Computer In Safe Mode;
Free Online Encyclopedia

Yes. I had seen this solution in the forums before and tried it, but it still used up the same amount of memory even in Safe Mode. I also removed several add-ons and plug-ins, have the default theme, and tried limiting cookie storage and memory usage in the settings.

Any other ideas?

I've called the big guys to help you. Good luck.

Thank you.

Create a new profile to test if your current profile is causing the problem.

See "Creating a profile":

• https://support.mozilla.org/kb/profile-manager-create-and-remove-firefox-profiles
• http://kb.mozillazine.org/Standard_diagnostic_-_Firefox#Profile_issues

If the new profile works then you can transfer files from a previously used profile to the new profile, but be cautious not to copy corrupted files to avoid carrying over problems.

• http://kb.mozillazine.org/Transferring_data_to_a_new_profile_-_Firefox

You can check for issues caused by plugins.

• set plugins to "Ask to Activate" on the about:addons page ("3-bar" menu button or Tools > Add-ons > Plugins)
• plugins are not affected by Firefox Safe Mode

I tried making a new profile and left Firefox running with a page open. Sure enough, its memory usage began climbing, though not quite to where it was. I have run some additional virus scans recommended in your post to remove some bad files, and have set Flash Player to Ask to Activate, not sure if that works yet. As I type this Firefox is pushing 400k kb with six tabs open.

What web pages do you have open? Try with just one page. After a time, open a second. Later, a third.

One tab isn't bad, but opening a second tab increases the CPU usage by 15-20%. Leaving this tab open with an email application open as well increased Firefox's memory usage from 285k to 320k kb. Additionally, this problem with it increasing my memory usage to unreasonable levels is new to the past two or three months.

Are there clips or many pictures? Please post some of those links so we can check them out.

Facebook and Youtube are common for me, but this morning when I replied it was this page and Outlook email. I can also leave it open only on pages without pictures such as http://www.metal-archives.com/release/upcoming and achieve the same result of the memory usage increasing dramatically as I leave the page open.