Useful about:config settings

Here you can find some useful settings to change in About:config page.

The most relevant to note should be:

Enable the use of userChrome.css and userContent.css -> toolkit.legacyUserProfileCustomizations.stylesheets to true

Most of the functions of TMP can be replaced with CSS or JS like multi-row tabs, keep the close button on tabs always visible, focus tab on hover, and color-coding tabs when they are loaded, unloaded (CSS Tweaks section, inside Tab-related-Tweaks.css), or through extensions like Tab Session Manager and Undo Closed Tab. For the ones that can't, here are some about:config settings that fix a few of them:

To keep FF open even after closing the last tab -> browser.tabs.closeWindowWithLastTab to false.
To open a search result typed on the URL bar on a new tab -> browser.urlbar.openintab to true.
To open a search result typed on the search bar on a new tab -> browser.search.openintab to true.
To open bookmarks on a new tab instead of the current tab -> browser.tabs.loadBookmarksInTabs to true.
To force popups on new tabs instead of windows -> browser.link.open_newwindow.restriction to 0 (should be 2 by default).
Open related tabs (the ones you open) as the last tab in the tab bar -> browser.tabs.insertRelatedAfterCurrent to false.

Disable "Enable remote debugging" prompt when accessing the browser developer tools -> devtools.debugger.prompt-connection to false
Disable reader mode -> reader.parse-on-load.enabled to false
Disable Pocket -> extensions.pocket.enabled to false
Disable Media keys (the pause/stop/play buttons next to the volume controls when watching a video or audio, as well as pausing video/audio in firefox with media keys) -> media.hardwaremediakeys.enabled to false
Disable service workers (used for website notifications mostly) -> dom.serviceWorkers.enabled to false
Enable ICC v4 color management -> gfx.color_management.enablev4 to true
Enable color management everywhere -> gfx.color_management.mode to true
Prevent "other bookmarks" folder to appear to the right when it's not empty -> browser.toolbars.bookmarks.2h2020 to false
Prevent bookmark folders in the bookmarks bar to close after opening a bookmark -> browser.bookmarks.openInTabClosesMenu to false
Force enable "Recommended by Pocket" despite not having Pocket enabled, or not being in the supported regions for it (U.S., Canada, U.K. and Germany) to show -> browser.newtabpage.activity-stream.feeds.system.topstories to true (You can disable it in the same manner setting it to false)

If you have an SSD and want to change the cache folders somewhere else, you should add these settings with the new path:

These are all telemetry related.

browser.ping-centre.telemetry to false
toolkit.telemetry.archive.enabled to false
toolkit.telemetry.bhrPing.enabled to false
toolkit.telemetry.enabled to false
toolkit.telemetry.server to "" (By default is https://incoming.telemetry.mozilla.org)
toolkit.telemetry.firstShutdownPing.enabled to false
toolkit.telemetry.newProfilePing.enabled to false
toolkit.telemetry.reportingpolicy.firstRun to false
toolkit.telemetry.shutdownPingSender.enabled to false
toolkit.telemetry.unified to false
toolkit.telemetry.updatePing.enabled to false
extensions.experiments.enabled to false
datareporting.healthreport.uploadEnabled to false
browser.newtabpage.activity-stream.feeds.telemetry to false
browser.newtabpage.activity-stream.telemetry to false

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