Firefox 4 requires at least OS X 10.5. You can get the latest version of Firefox 3.6 from http://www.mozilla.com/en-US/firefox/all-older.html

When you re-install Firefox 3.6 it will use your existing bookmarks.

Mozilla are working to prevent Mac users with non-compatible systems from getting the notification about Firefox 4, and also not displaying the "Download Firefox 4" button on http://www.mozilla.com

Thanks Tony, that reply was so fast it's like you're my flatmate!!

Seeing as the Upgrade download page opened itself (I didn't go looking for it) and had/has the text I quoted ("all systems") I felt happy to go ahead with the upgrade. I'm used to other software upgrades not being good for my old OSX4.11 so I look out for that. This is a bit careless of whoever wrote the text for the Upgrade page, it's not too hard to write "for OSX 10.5 or later", is it? If I'd seen that I wouldn't have downloaded the upgrade.... moan moan.... Thanks again Tony Dave in Cork

I totally agree, there have been many Mac users that have been effected by this.

Thank god for that! Firefox back up and running (with all my precious bookmarks). Come the great day I hand over €130 to Apple for their latest system I'll upgrade to Firefox 4! Thanks for your rapid assistance Tony!

Thank you very much TonyE. Very, very much.

You know, since a lot of people seem to be running into this issue (my wife just had this problem), the easy hotfix would be to post a message on the home page that says NOT COMPATIBLE WITH MAC OSX 10.4.11. MUST BE MAC OSX 10.5. Because I looked all over your site and I couldn't find a list of (non)compatible os's.

http://www.mozilla.com/en-US/firefox/4.0/system-requirements/

Mac Operating Systems

• Mac OS X 10.5
• Mac OS X 10.6

Recommended Hardware

• Macintosh computer with an Intel x86 processor
• 512 MB of RAM
• 200 MB hard drive space

I have 10.6.7 and ever since I installed firefox 4, I cannot open firefox at all, nor can I reinstall 3.6. It says that I already have firefox installed and running and I cannot install another one. It says I cannot delete it and I am totally stuck. docjb

Good info edmeister...thanks. Though in this case, seems too little too late, lol.

The problem most people are having (myself included) is that this info needs to be readily and easily available BEFORE we download FF4 and find out it's incompatible w/our OS. We can all click on the link you posted, but my question is HOW did you find it in the first place? I made a concerted effort to look, and still didn't come across it.

Can I simply get a link on the download page for "System Requirements"...?? A tiny little link in the footer? A one liner somewhere specifying "for MacOSX 5 or higher"...? I don't ask for much, really I don't.  :)

I also have OSX 10.6.7, was very happy with FF3.6 and all FF3 updates. Saw link to FF4 and could not imagine it would be as bad as it is. Tried installing it to a different applications folder, but it seems to have taken over the FF3.6.16 update I'd only been using a few hours, which is now "called" FF3.6.16 but behaves like FF4. I'm afraid to simply eliminate them and re-install the FF3.6.16 dmg for fear of disaster. Just want to know how to get back!

I'm appalled that the system requirements are not made clear on the download page for 4.0. Why does Mozilla say "for all systems" when it's not true? Like the rest of you, I also downloaded 4.0 only to discover that it wouldn't work on my system, and then I spent a stressful half hour thinking that I'd totally f'd up my browser and lost all my bookmarks, etc etc. It was not easy figuring out how to restore Firefox 3.6 either. I'm grateful to those of you who posted this info. No thanks to Mozilla though.

I like Firefox, but I'm really unimpressed with Mozilla's negligence on this. It would be the simplest thing for them to post a clear message about the Mac system requirements. Why on earth don't they do so.

P.S. I was able to restore Firefox 3.6.* by downloading it from this site:

http://www.mozilla.com/en-US/firefox/all-older.html

edit: Fixed link as the unofficial oldaps site was not needed and because 3.6.13 was insecure and the 3.6.18 was current version then.

Nice save icosh! I was trying without success to use the newest 4.0 version of FF. It would not install on my Imac with 10.6.7 OS, and when I tried to use it, I couldn't go from an email link, directly to the page referenced. I was having to give it two keystrokes to get to the link.

Also whenever I tried to go to these links, I got a page moved error each and every time.

So I came here and used your solution! So far so good, and I am not updating Firefox, this year, unless something stops working.

Thank you, Thank you, and yes, one more Thank You!

Intel chip is NOT recommended, it is REQUIRED. I am running 10.5 on a PPC so cannot use FF4. And I can't figure out how to revert to 3.6.18 that was auto updated today to 3.6.19 which does not work.