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How can I diagnose the problem behind the delay I get when changing tabs in Firefox? It is up to about 1.5 seconds.

To provide some background, I use three monitors and often have three Firefox windows open at the same time. My machine should be fast enough, it is a AMD Phenom II X6 1055T at 2.8GHz, a NVIDIA GeForce GTX 660 and 4GB of RAM.

The issue appears to be stronger for some webpages. For example, the Wordpress backend, the FireFTP addon tab, Google Mail, are slower than simple pages like Google Search, or static HTML pages.

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Assuming Windows: check Task Manager, Resource Monitor, Process Monitor, etc. – Ƭᴇcʜιᴇ007 Aug 7 '13 at 13:28
@techie007 It consumes about 380MB RAM which stays relatively constant. CPU load is very small, around 8% or less. In idle only around 0.5%. My system at all uses 1.7GB of 4.0GB RAM. My operation system is Windows 8 x64. What further information could be useful? – danijar Aug 7 '13 at 13:32
And these are the numbers from during the period you are experiencing the slowness in question? Have you tried disabling all your FF plug-ins and extensions to see if the problem subsides? – Ƭᴇcʜιᴇ007 Aug 7 '13 at 13:36
These numbers are during slow reacting user interface, yes. I have a lot of plugins. I will try disabling all of them later on today. – danijar Aug 7 '13 at 13:38
up vote 2 down vote accepted

The scripting console provided by the Firebug addon caused the performance issue. I only noted that when reading a notification integrated into the extension, stating that this is a known issue and will be fixed soon.

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Users on reddit echo your thoughts:… – SeanDowney Oct 10 '13 at 15:07
@SeanDowney Thanks for posting that, I guess its a coincidence. But interesting anyway. – danijar Oct 10 '13 at 21:50
Is Firebug integrated into Firefox or is it an extension? – Caterpillar Feb 25 '14 at 16:49
@Caterpillar Yes, I already stated in the question that it's an addon. Next time, please use a search engine for such basic facts. – danijar Feb 25 '14 at 18:40
@Caterpillar Alright. The Firebug extension is still very popular, although Firefox comes with own integrated development tools. – danijar Feb 25 '14 at 19:43

It sounds like you end up having to wait for something that is not related to CPU/memory, unless your computer in general is performing badly for some reason, but if you have lagg when scrolling, you may have video driver issues.

What you might end up waiting for is probably the mass storage, if you are using an SSD this would only happen if windows for some reason is shutting it down, you should be able to adjust such settings from the power options advanced part.

If you are using a HDD this might be of a similar nature, with the HDD being powered down to save power. Or, it is simply how long it takes for the cache file to be read. Try crystal Disk Mark to see how well your drive is performing, and you might try to find a setting in firefox to make it use more ram and rely less on cache.

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Scrolling is smooth and I can run high performance graphics application on my computer with good performance. I use a SSD as my primary drive, both the Firefox installation and its Application data is stored there. The idea about caching is interesting, maybe it's not about cache file on the drive, but in memory? – danijar Aug 7 '13 at 13:59
If the tabs are in memory they should load very fast, and if cached on an SSD it should be very fast too, does the delay happen regardless the complexity of the page you are switching to? Also, do you get the same if you try having IE10, FF and Chrome on the different monitors? that should be heavier, so if you dont get the same delays there is some problem with either FF or a FF plugin – Nisse Aug 7 '13 at 14:06
you might want to check whether any of your plugins are writing to disk. If some plugin is writing to disk regarding the state of things in one FF window, and then the same from another FF window but to the same file, it might end up locking for a little while and 1second might be waiting for such a write attempt to time out. Seems a little bit too noobish of a developer to do that, but still, something related might be possible. – Nisse Aug 7 '13 at 14:27
I tried disabling all addons without success. But it might be related to the flash player. Youtube tabs tend to show up later than most other tabs. Chrome is much faster with the same tabs open. For testing this I opened twenty web applications on first Firefox, changed between tabs, and then exited Firefox and tried the same with Chrome. – danijar Aug 7 '13 at 16:47
have you tried reinstalling FireFox? maybe installing an older version could work too.. in the try with 20 tabs you mentioned was that in one FireFox window? – Nisse Aug 10 '13 at 9:36

In my case, it was due to an extension called QuickShare Widget. I disabled it and tabs and close button started to work just fine!

To disable, go to Tools-->Add-Ons-->Extensions, then disable the QuickShare Widget.

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There is a firefox subreddit thread that says that the tab switch slowness is due to switching back and forth between firebug and non-firebug tabs. And a possible resolution is listed:

For me, the workaround (sort of) was to realize that the main culprits in this are the "console" and "net" tabs in Firebug (*). If you disable those tabs (only enable them when you really need them), you'll make Firebug actually quite fast.

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