See this report for Add-ons that were downloaded from the official Mozilla Add-ons website.
https://addons.mozilla.org/en-US/firefox/compatibility/report

You're on you own for Add-ons that you obtained elsewhere.

While you at it, check for Firefox 6 compatibility, it is going to be released in a few days.

A few months ago I was able to automatically check my add-ons just prior to downloading Version 4. It said 3 of my 18 add-ons were not compatible. Since I NEEDED those 3 add-ons, I declined to get Version 4. Now the option to automatically check add-ons before accepting a new version of FF is not available (or possible). I wish the option to automatically check add-ons against a newer version of FF was still available. It was a great help.

I looked at the link suggested above. I don't mean to be rude, but the page for the Add-on Compatibility Center seems worthless and/or confusing to me (and I write User Manuals for data input for 2300 employees). There is no explanation or legend of HOW to read the chart.

1) Is the page a compatibility chart for only Version 5?

2) The numbers in the green ovals... is that the version number for each add-on that works in Version 5 of FF?

3) Most of the ovals are green. A few are gray. One is yellow. What is the difference in color?

4) Some of the values in the oval have an asterisk. I presume it means there's an exception, but I don't see any footnotes (or does the asterisk mean all versions from the value listed going forward?)

5) The bar graph is terrible:

5a) The add-ons are ordered by usage size. Most used to least used? or least used to most used?

5b) Adblock Plus has no gray, then a green bar that takes up about 10% of the whole width. Does it mean that about 10% of users using Adblock have the version listed?

5c) Some bars have a gray and green bar. Video DownloadHelper for example. About 20% of the whole length of the bar is gray (Does that mean 20% who use the add-on are NOT using the version listed?). The green bar is about 5% of the whole length (Does that mean 5% ARE using the version listed?)

If all of the Extensions you are using are hosted at addons.mozilla.org then just search for each of the extension you have in order to see if recent version lists 5.0 or newer as compatible is not listed in that compatibility chartwhich links to extensions page for each. Go to bottom of page for each extension to view the Version information and to click on View all versions in case there is a newer release not yet ready for public. The versions used to be listed more at top but Mozilla changed the look of addons.mozilla.org again.

Since you are using 3.6.18 and if you have not done any extension updates recently, then the versions of the extensions you have may likely be older.

https://support.mozilla.com/en-US/kb/Add-ons+are+disabled+after+updating+Firefox

Addons just so you know is really just a word that lumps together Extensions, Themes, Personas, Plugins, dictionaries, search engines.