ST00P!D M0NK3Y  Don't know why they're posting that as the minimum requirements. I have 13 tabs open and it's using 80MB of RAM... the app itself only takes up 50MB of space.  
(Version 3.5)

NEONBLUE2  It should probably be noted that Firefox 3.5 requires Tiger. In order to run Tiger you must have at least 256MB of RAM anyway.

Windows 2000, on the other hand, requires 64MB of RAM and is the Windows minimum requirement.  
(Version 3.5)

ST00P!D M0NK3Y  Opens in 1.5 - 2 seconds for me and runs insanely fast. Safari runs fine for me too.  
(Version 3.5)

ROBOTANK  Firefox also takes a long time to start for me. I used to have too many extensions.I got rid of most of them, but I didn't notice any substantial improvement in loading time. I hate FF's long load time: It makes it feel bloated, and makes Safari feel like a far more streamlined browser.  
(Version 3.5)

MACFOOL  About 2 seconds to load on a Dual G5 10.5.7 and maybe 3 seconds on a new 4 GB Mini 10.5.7

Y'all got something wrong.  
(Version 3.5)

BOSSA-NOVA  First launch of Firefox after a RESTART of the computer?  
(Version 3.5)

BRUCEANDERSON  Part of Safari is running in the system itself, so its initial launch time is shorter. Firefox has to bootstrap itself. After the first launch after a reboot FF should start about as quickly as Safari does.

But I'm wondering how often do you restart your computer for this to be a significant issue?  
(Version 3.5)

BOSSA-NOVA  I work a lot with photos, like in Lightroom. After a while computer gets very slow, so I reboot it from time to time.  
(Version 3.5)

MACFOOL  BOSSA-NOVA - Had to wait until I needed to Restart to respond to the question. Firefox 3.5 takes 4 seconds or a little less to open from launch on both machines subsequent to a Restart or Cold Boot.

If this has any bearing (probably not) I run all non-Apple applications from a second partition that will let me install there.

The fact you think you must reboot so often may be the source of your slow launching?

Both Firefox and Safari launch VERY fast give or take a few hundred milliseconds.

Try a cold start into a PRAM zap (thrice) to a Safe Boot, run Permissions repair in Disk Utility, then run your maintenance scripts, trash all caches and then Restart. If things are still slow, well, good luck.

Hope this helps.  
(Version 3.5)

BOSSA-NOVA  Firefox 3.5 only takes so long (about 30 seconds) to launch when I first open it after a restart of the system. Subsequent launches while the system is running only take 3 seconds.

I just want to know if others experience the same.  
(Version 3.5)

JAN13  That is exactly what I am talking about .... it sloooooow ...  
(Version 3.5)

IMHO  BRUCE ANDERSON

I restart my Mac at least every day. And almost every day a second time, when I'll be away of my Mac for some hours. Energy saving, you know. You don't mind about energy shortness and the environment?  
(Version 3.5)

ST00P!D M0NK3Y  I'm surprised that Safari is taking 5 seconds to start for you, let alone Firefox taking 30+ seconds. It takes both Firefox and Safari only 1.5-2 seconds to open for me even after a restart. Maybe you should consider reformatting your Mac. I do that every once in a while when nothing else seems to work.  
(Version 3.5)

ROBOTANK  If I'm not mistaken, Fast Dial is an extension, not a default feature of Firefox? That isn't clear in your post.  
(Version 3.5)

CROPP  Select FF3.5.app, -> Show Package Contents -> Contents

Open PKginfo in TextEdit and change "-n APPLMOZB" to "APPLMOZB".

It works, I did it.

Do it at your own risk though, because I have absolutly no clue on what it could interfere with...  
(Version 3.5)

DOUG ENGELBART  Thank you, thank you, thank you, CROPP! ^^ I did it as you told me. Now my mousedriver 'USB Overdrive X' works fine with FF3.5 just like with every other app. As it should be.

Additional tips:

(1) Close Firefox before doing this.

(2) Be sure to erase the '-n ' in front of the capitals AND the CarriageReturn after them (as it is in Firefox 3.0.11 and before). Then save and close the PkgInfo file.

(3) Duplicate the so modified Firefox application, then trash&delete the original. Rename the duplication from 'Firefox copy' to 'Firefox' or 'Firefox 3.5' etc. and use only it.

P.S.: I reported the bug to bugzilla. Hope they'll avoid such an awkward bungling in the future.  
(Version 3.5)