NO ! ! ! Sync is meant only as a way to share data between different profiles/computers.

If you are that worried, copy your files to a thumb drive and take it with you.

Even if Sync worked perfectly, not all data is synchronized. You can test what a rebuild might feel like by creating a new Firefox profile and signing it in to your existing account. You might want to make a backup of your current profile folder first "just in case."

• Back up and restore information in Firefox profiles

New Profile Test

This is quick to set up, but Sync isn't instant, so you may need to leave this window in the background and wait a while to get the full picture.

Inside Firefox, type or paste about:profiles in the address bar and press Enter/Return to load it.

Take a quick glance at the page and make a mental note of which Profile has this notation: This is the profile in use and it cannot be deleted. That is your current default profile.

Click the "Create a New Profile" button, then click Next. Assign a name like May2021, ignore the option to relocate the profile folder, and click the Finish button.

Firefox will switch your default profile to the new one, so click the Set as Default Profile button for your regular one to avoid an unwanted surprise at your next startup.

Scroll down to May2021 and click its Launch profile in new browser button.

Firefox should open a new window that looks like a brand new, uncustomized installation. (Your existing Firefox window(s) should not be affected.)

After you sign in to your account, Firefox will Sync in the background. Meanwhile, you can continue working in your regular profile window(s).

How well does it work for your needs?

When you are done with the experiment, you can close the extra window without affecting your regular Firefox profile. May2021 will remain available for future testing, or you can delete it on the about:profiles page. (Carefully -- don't delete your main profile!)