I've installed so many add=ons on firefox 3, but when I changed to firefox-4 these add-ons are not compatable.
The addons I've installed were crawler tool bar, zone alarm tool bar, you tube downloader etc....
Wšě wotmołwy (1)
There are many video downloaders that work with Firefox 4, such as Flash Video Downloader (Youtube Downloader) and Easy YouTube Video Downloader.
For other add-ons you need to check with the developer to see if they have released any updates to their add-ons. For those that have no been updated you can check the Mozilla add-ons site to see if there is an alternative.
For the compatibility of many common add-ons see https://addons.mozilla.org/en-US/firefox/compatibility/report - those listed as either 4.0.* or 4.2a1pre will work in Firefox 4