This works fine on Firefox so it's not a bug.

Can you try to start Firefox in Safe Mode to see if Firefox works properly with no error? You can start Firefox in Safe Mode below:

• Windows/Mac: Go to Help > Restart with add-ons disabled
• Linux: Run firefox -safe-mode in the Terminal/Konsole

If Firefox opens up fine with no problems, it's probably one of your extensions that's causing the issue. You can re-enable your add-ons one by one until you find the one that causes the issue upon being re-enabled.

It's important to update Flash, you're currently at the outdated version 11. You can get the newest below

• https://get.adobe.com/flashplayer

Wow, quick answer, thanks ! I've tried restart Firefox in Safe Mode, Firefox starts properly. But i've same issue on drag and drop in Safe Mode. What can I do ?

You can try these steps in case of issues with web pages:

You can reload web page(s) and bypass the cache to refresh possibly outdated or corrupted files.

• Hold down the Shift key and left-click the Reload button
• Press "Ctrl + F5" or press "Ctrl + Shift + R" (Windows,Linux)
• Press "Command + Shift + R" (Mac)

Clear the cache and cookies only from websites that cause problems.

"Clear the Cache":

• The image "new fx menu" does not exist. > Options/Preferences> Advanced > Network > Cached Web Content: "Clear Now"

"Remove Cookies" from sites causing problems:

• The image "new fx menu" does not exist. > Options/Preferences > Privacy > "Use custom settings for history" > Cookies: "Show Cookies"

I cleared the cache and a lot of cookies : always same issue. Is it easy to return to the previous version of Firefox ? I am a developper and I need the Drag and Drop feature.

PROBLEM SOLVED.

My apologies, the problem was in the partner script (jquery.gridster.js), on the line where the touch feature is tested.

[ For Gridster users : line 431 in jquery.gridster.js, replace var isTouch = !!('ontouchstart' in window); by var isTouch = false; ]

Now everything works fine.

And thanks to the Firefox team, the 29th version is so good !