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I would like to know of addons which actually enhance firefox's performance, both intentionally and unintentionally. I find that firefox tends to have major performance issues with certain websites. These websites tend to have a fair amount of javascript and css, and probably a large dom tree which may even be growing dynamically through javascript too. The worse offenders are those with heavy javascript, use heavy facebook integration, websites with non performant javascript, excessive javascript and websites with too many advertisements.

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closed as too localized by bwDraco, Ƭᴇcʜιᴇ007, random Nov 26 '12 at 0:02

This question is unlikely to help any future visitors; it is only relevant to a small geographic area, a specific moment in time, or an extraordinarily narrow situation that is not generally applicable to the worldwide audience of the internet. For help making this question more broadly applicable, visit the help center.If this question can be reworded to fit the rules in the help center, please edit the question.

Not really an add-on because it's integral to Firefox: click-to-play. This isn't yet enabled by default since it still has rough edges but one can go into about:config and change plugins.click_to_play from false to true. I've been using it for a couple of months. – user151227 Sep 19 '12 at 15:01
@vasa1: Would nice if you said what click-to-play does/controls... – martineau Sep 19 '12 at 15:19
@martineau, click-to-play, if enabled, prevents plug-ins from running automatically. The user has to click on the icon representing a plug-in to let it function. Plug-ins would include things like Flash, Quicktime, and Java. – user151227 Sep 19 '12 at 16:10
community wiki? – n611x007 Nov 23 '12 at 1:13
@DragonLord I think it is a valid question. I simply thought that it would be formally/technically more useful as a community wiki. – n611x007 Nov 23 '12 at 2:08

AdBlock Plus and NoScript will both block the types of annoyances you mentioned.

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There are two things which can slow Firefox down:

The javascript and extra stuff which you already mentioned and slow external web sites.

NoScript and AdBlock and will help a lot with the first.

RequestPolicy and Ghostery help with the second part, where Firefox is waiting on part of the webpages from other servers. Often from add servers who do not seem to care about speed. (Or to be fair, end user speed is not their primary goal).

Another nice plugin is FlashBlock. It prevents flash movies from automatically starting. If you have a low bandwidth connection to the net then this will help.

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I believe you should try AdBlock Plus and FlashBlock. Works well for me. In some cases, if it's still not enough performance, you may also consider using Opera browser with it's Opera Turbo mode.

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AdBlock Plus is the most obvious answer... I'd recommend using Element Hiding Helper for Adblock Plus, which greatly helps selecting the visible content that you want to get rid of.

Noscript is a great addition to preven execution of Java and JS.

Ghostery is also quite useful and blocks a lot of tracking elements (including most social media buttons).

You can also try MemoryFox to attempt to reduce the browser memory usage (however there were controversies about the real improvements).

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For me I use this freeware, with all these add-ons (AdBlock, etc.): Firemin

... and actually do decrease Firefox memory usage, up to 95% (under 1MB in some cases). Firemin has not received any negative reviews and no side effects like browsers crashing have been reported, “knock on wood” ....

For me it's true – I can open multiple tabs and many profiles without experiencing hangs much and now my Firefox crashes less than before.

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This is an experimental extension to save CPU (battery) time and make the browser more responsive. It suspends actions in background tabs until they become active again.

By Wladimir Palant, the author of Adblock Plus.

Many addons fast up Firefox as a side-effect. The following ones are mostly duplicated from other answers:

  • Adblock is also good as it blacklists many flash ads, cross-site requests, javascripts.

  • Ghostery is for privacy what Adblock is for ads, blacklisting tracking, statistics, etc. and has the same side-effects on CPU time. (Personal favourite addon.)

  • RequestPolicy is explicitly for cross-site request control. (From Hennes' answer!)

  • From vasa1's comment: the plugins.click_to_play setting in about:config can be used to disable plugins (flash/java/etc.) until you click on a placeholder icon.
    (Side-note: the same idea is around in Opera Browser's On-demand plugin or ODP since 2010.)

  • I also like to use QuickJava to manually (as in snail) disable JS/Java/Flash/etc. when I feel like it. I prefer it over the more powerful (and automatic) NoScript, for NoReasonTM.

experience: RequestPolicy needs a little accustomization from you to it, in order to be useful. First time you install it, all you get is strangeness - like css and images not loading, and you wonder is this empty page at google the same stuff I should (and used to) get, or did I just get a malware attack blocking my net? If you feel like this, relax, it's not a malware, it's the opposite - it's YOU back in control, again - it's just strange, at first!

Why do my eyes hurt?
You've never used them before.
                      --Neo & Morpheus, The Matrix

Search & find the icon of RequestPolicy a Red Flag (in the statusbar (Ctrl+/), for example), at least it's red when it's actively doing sumthin'.

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