What problem(s) are you experiencing that makes you think you need to use Reset? Be specific.

You will need to reinstall your Extensions and Appearance items (themes/personas). Read the following thoroughly including the links in the article for a full understanding. A copy of your old profile will be saved to your desktop as "Old Firefox Data". There is a link in the article providing information on how to transfer data files (not the whole folder) from that desktop copy to your new profile. Carefully copy a few at a time and test to be sure that your problem is not re-occurring.

• Reset - http://support.mozilla.org/en-US/kb/reset-firefox-easily-fix-most-problems
• You can also backup your profile to another disk/device/CD or DVD or USB drive before the Reset, just to be safe - https://support.mozilla.org/en-US/kb/back-and-restore-information-firefox-profiles

Yes, you will have to reinstall all extensions if you reset Firefox.

If you reset Firefox then a new profile is created and some of your data (bookmarks, passwords, cookies, form data) is automatically imported and your current profile will be moved to the desktop (Old Firefox Data).

You can recover more data from the old profile (be cautious with doing that).

Did you try Safe mode to see if that has any effect?

Start Firefox in Safe Mode to check if one of the extensions (Firefox/Tools > Add-ons > Extensions) or if hardware acceleration is causing the problem (switch to the DEFAULT theme: Firefox/Tools > Add-ons > Appearance).

• Do not click the Reset button on the Safe mode start window or otherwise make changes.

• https://support.mozilla.org/kb/Safe+Mode

You can also try to clear some personal data like the history if you currently have large website history and the cache.

• https://support.mozilla.org/kb/Clear+Recent+History

Note that clearing "Site Preferences" clears all exceptions for cookies, images, pop-up windows, software installation, and passwords.

If it is a big difference compared to other browsers then also check your security software.