I think you can ease most of the load. Let's say Windows recognizes your external drive as "E". If you create a new profile on E drive, then nearly all disk updates will be done on the E drive (major exceptions that come to mind: loading of Firefox itself and plugins).

You can test this without losing any data, as follows -- I'm assuming Windows:

Overview

These are the steps:

1. Open a window on your current Firefox profile (later you'll copy from this window)
2. Create a new Firefox profile
3. Remove everything from that new profile folder
4. Copy in everything from your current profile folder

Open your current Firefox profile folder

Open the Troubleshooting Information page using either:

• "3-bar" menu button > "?" button > Troubleshooting Information
• Help menu > Troubleshooting Information
• type or paste about:support in the address bar and press Enter

In the first table on the page, click the "Show Folder" button. This should launch a new window listing various files and folders in Windows Explorer.

Leaving that window open, switch back to Firefox and Exit, either:

• "3-bar" menu button > "power" button
• (menu bar) File > Exit

Allow 10 seconds or so for Firefox to shut down.

Create a new Firefox profile

Start up Firefox in the Profile Manager by pasting the following into the Start menu search box, or the Start > Run dialog, and pressing Enter:

firefox.exe -P

Note: Any time you want to switch profiles, exit Firefox and return to this dialog.

Click the Create Profile button, assign a name like Relocated, and click the Choose Folder button. Navigate to your external drive and create a new folder for your Firefox profile. IMPORTANT: make absolutely sure to select the new empty folder; do not choose an existing folder containing files of any kind. Then click Finish, select that new profile in the dialog, and start Firefox.

Open the New Profile folder in Windows Explorer

Firefox in the new profile should look like a factory fresh installation. Open the Troubleshooting Information page using either:

• "3-bar" menu button > "?" button > Troubleshooting Information
• Help menu > Troubleshooting Information
• type or paste about:support in the address bar and press Enter

In the first table, click the "Show Folder" button. Firefox will launch your brand new profile folder in Windows Explorer.

Leaving that folder open, switch back to Firefox, and Exit. When Firefox closes, the profile folder should be front and center, or you can activate it using the Task bar.

Copy Old Data in Place of New

In that new profile folder, select all the contents (Ctrl+a) and delete. IMPORTANT: make sure it's the new folder on the external drive and not your current profile folder!

Leaving that window open, switch over to your current profile folder. Select everything (Ctrl+a) and Copy (either right-click > Copy or Ctrl+c).

Switch to the empty new profile folder in other window and Paste (either right-click > Paste or Ctrl+v). This may take a minute since some of the files are large.

Start Firefox

Firefox should start up in that new profile with the data from your live profile. (The cache will not be copied, but will be rebuilt as you browse.)

Success?

Thank you so much @jscher2000 for the lightning quick assist. Success! At first it would not work and kept re-starting as a new install because I was still running Firefox 35 and when I checked for version info it automagically updated itself to 37.0.1, and now it starts from the D: drive as if it was starting from the c: drive, and seems like the internal c: drive access is now minimal.

I also noticed my ini file was deleted with the upgrade and it probably was not working with v35 because I probably would have had to edit it. (Isrelative and path). Again, thank you so much, I really wanted to run it as before with all my saved history as I always run with 22 tabs open and never clear my history, cache or cookies, and is probably why it takes 3-4 minutes for my c: disk activity to stop (maybe firefox closing its open files) after I shut down firefox. This seems to be doing what I want it to do!