Please download the free version of Malwarebytes from http://www.malwarebytes.org/products/malwarebytes_free and then run a full system scan to eliminate malware as the culprit.

You should also uninstall the Java Consoles dating back several years since these pose a security risk. Disable them first in Tools | Add-ons | Plugins and then uninstall via Add/Remove Programs.

After you doing that, update to the latest version via http://www.java.com/en/

It still sucks, my mouse slows down to a crawl and gets real choppy, also my key strokes slow down, also any time firefox 4 is running my machine becomes almost unusable and I am not running some peace of crap machine either. Firefox has really dropped the ball on this release I may have to stop using them all together if they don't get it fixed fast.

You can find a good selection of alternative browsers at Filehippo.com.

FF is no longer a viable browser. When they start babbling nonsense about malware you know they have run out of answers.

It's broke and they can't fix it.

I found the REASON to be Add-Ons. Though compatible, some of the updates for fox 4 just suck. I just disable many of them till I need them. I imagine by the time FF5 is ready the Add-ons for 4 will be better. BUT you can always re-load old versions.

ibdwl - You have the Firebug extension which is a renowned memory hog which should only be enabled when you are actually using it. Some experts have gone so far as to suggest you should create a separate profile with Firebug as the only add-on -

http://kb.mozillazine.org/Problematic_extensions

If you have persistent problems you should do this trouble shooting -

https://support.mozilla.com/en-US/kb/Troubleshooting%20extensions%20and%20themes

It is not only Firefox that has been updated, so have many extensions, plug-ins(such as Flash), toolbars, A/V programs etc. New problems and conflicts can arise.

SkyWriting - I have 30 extensions which have all been updated for some weeks. If your extensions won't work on Fx4 you can sometimes find a new version on the developer's website. Very often, there are alternative extensions which are sometimes better and certainly better maintained.

I tried all that the simple fact is that this release of firefox came out way to early with far to many bugs in it. I have went back to version 3.6 and will stay there until they get their act together.

As far as "fire bug" goes I use it everyday and without it there would be know reason for me to use FireFox.