Firefox under Linux is slowing down during usage

I recognized a slowdown of Firefox during surfing. After a programme restart all was fine again but slowdown occurred again. This is what I did to resolve the problem.

• Inactivation of all addons not in much use
• Inactivation of all greasmonkey scripts not in much use
• Changing preferences of "Link Alert": inactive status for links and images

• Changing Firefox settings in "about:config":
• extensions.s3downbar.function.useAnimation;false (this can also be changed through the preference page of Download Manager (S3))
• browser.tabs.animate;false
• browser.fullscreen.animate;false
• browser.download.animateNotifications;false
• toolkit.scrollbox.smoothScroll;false
• extensions.treestyletab.tabbar.scroll.smooth;false

Firefox, some settings

• Allow unsigned extensions / addons

about:config ➪ xpinstall.signatures.required ➪ false

• Horizontal tabs
• enable OpenGL OMTC go to about:config and set:

about:config ➪ layers.acceleration.force-enabled ➪ true
about:config ➪ layers.offmainthreadcomposition.enabled ➪ true (default)

• Turn off the disk cache

Preferences ➪ Advanced ➪ Network ➪ "Cached Web Content: Override automatic cache management" on ➪ "Limit cache to" 0

• load multiple tabs in the background:
  change in about:config "browser.sessionstore.restore_on_demand" to false

Kudos go here.

P.S.: Firefox add-ons

• "Colorful Tabs" does not work well together with other add-ons that effect tabs.
• The Greasemonkey script "Linkify Plus Plus" severely slows down the browsing experience. (This may be dependent on other add-ons that manipulate links.)