Any particular add-on? Maybe there's an updated version or substitute?

If you can't find a solution with Firefox 4, here's the process to roll back:

First, I recommend backing up your Firefox settings in case something goes wrong. See Backing up your information. (You can copy your entire Firefox profile folder somewhere outside of the Mozilla folder.)

Next, download and save Firefox 3.6 to your desktop for future installation. http://www.mozilla.com/firefox/all-older

Close Firefox 4.

You could install Firefox 3.6 over it (many have reported success) or you could uninstall Firefox first. If you uninstall, do not remove your personal data and settings, just the program.

Unless you have installed an incompatible add-on, Firefox 3.6 should pick up where you left off. If there are serious issues, please post back with details.

Note: I haven't actually tried this myself!

Firefox 4 has been out for almost 3 months now, and Firefox 5 is due to be released in the next week or so. If some of your extensions haven't been updated yet you should probably "kiss them off" as "abandoned" by their developer. At this late date, chances are they will never be made compatible with current or future versions of Firefox. You need to look for similar replacement extensions to use in Firefox4 and later versions, instead of clinging to the past.

Strongly agree with the-edmeister. I have about 30 extensions and they have all been updated for weeks and weeks.

For ones you especially value you could go to the developer's home page to see if there is an update. Searching in add-ons will often produce better extensions; certainly better maintained.

If you name a few we may be able to help you find replacements. Often there are 3 or 4 extensions that do much the same thing.

Please report back.