select Command Prompt (Admin). Type "SFC /SCANNOW" (without quotes or copy/paste) and press Enter. For more information on using SFC, please refer to the Microsoft KB: Use the System File Checker tool to repair missing or corrupted system files Check to see if getting what you pay for from your ISP http://www.speedtest.net/ Open Device Manager and find Network Card and right Click and Update. If says using latest one should take the name and google it and see if newer drivers and what the top speed of it is as time may have passed it by. https://support.mozilla.org/en-US/kb/quick-fixes-if-your-firefox-slows-down https://addons.mozilla.org/en-US/firefox/addon/speed-tweaks-speedyfox/ If nothing above helps : Please Refresh but do this 1st: *https://support.mozilla.org/en-US/kb/export-firefox-bookmarks-to-backup-or-transfer *https://support.mozilla.org/en-US/kb/back-and-restore-information-firefox-profiles then *https://support.mozilla.org/en-US/kb/refresh-firefox-reset-add-ons-and-settings TEST....... If no issues then Extensions which need to be added back in 1 at a time and tested ..... Or it is your Profile : Make a new one and test ...: *https://support.mozilla.org/en-US/kb/profile-manager-create-and-remove-firefox-profiles If is your Profile : *https://support.mozilla.org/en-US/kb/recovering-important-data-from-an-old-profile *http://kb.mozillazine.org/Transferring_data_to_a_new_profile_-_Firefox Note: Any customization will revert back to default, you will also need to reinstall Extensions. If explain what you do not like is possible to help you as over 2million possibilities to look/feel. Though all that code is not around but some is. https://www.howtogeek.com/333805/how-to-change-or-customize-firefoxs-new-tab-page/ https://www.howtogeek.com/333110/how-to-customize-firefox-quantum-and-remove-the-white-space-around-the-title-bar/ https://www.howtogeek.com/334716/how-to-customize-firefoxs-user-interface-with-userchrome.css/ https://www.howtogeek.com/334716/how-to-customize-firefoxs-user-interface-with-userchrome.css/ http://techdows.com/2017/09/classic-theme-restorer-userchrome-css-modify-firefox-57-photon-ui.html https://github.com/Aris-t2/CustomCSSforFx/issues/1 https://www.accessfirefox.org/Theme-Font-Size-Changer.php https://www.userchrome.org/ https://www.accessfirefox.org/Firefox_Accessibility_Themes.php https://www.userchrome.org/what-is-userchrome-css.html http://kb.mozillazine.org/UserChrome.css https://github.com/axydavid/FirefoxUI/blob/master/README.md https://github.com/wilfredwee/photon-australis https://www.reddit.com/r/FirefoxCSS/ Note not all code in one place. Please let us know if this solved your issue or if need further assistance.