This is one of the things I got accustomed to, so I almost forgot how annoying it is.
I use a lot of font zooming, because my eyes suck. Some pages (notably this one) ignore the default font-size I have set in firefox, so I have to zoom in.

(Font-zoom in Firefox is ctrl-mousewheel or ctrl-+)

Changing the font preferences (System-Preferences-Appearance-Fonts) to monochrome or maximum-contrast doesn't help. Even if it did, the fuzzy rendering is worse than the two to five seconds I have to wait for a zoom to take effect.

Anybody got any idea? You can probably test this yourself. When you do ctrl-mousewheel on a site with a lot of text, the cpu will go to 100%, and Firefox might even become unresponsive for a couple of seconds.

A complex layout makes things much worse. A lot of text on a simple page still is not very responsive, but it works much better. That might be an indication.

It has to be somehow related to Linux. Even in the virtual machine - firefox in windows zooms the fonts instantaneously

Sorry mine is as fast on Linux as it is on XP or Vista.

Cart

The fonts change size in a heart-beat.

Anyone have any ideas why it would be slow?

Memory? I tried two different distros - PCLinuxOS an Mepis both with Firefox and had no problems, the font size change was instant in both cases. I am operating with 512 meg.

I didn't expect that.

It was unbearably slow on my old pc, but it is still slow now. 1.8ghz Sempron, 1gig ram, Gforce7600GT... enough to play Quake4 on full graphics.

Well it's obviously the pc then. I had a couple of distros on this one and my old one... been through quite a lot of hardware in the meantime, so it pretty much comes down to the processor. But I have no performance problems with anything else. Right now I have about 20 windows open on 2 workspaces... including a guest OS... no complaints. Opera zooms reasonably fast, but I have other issues with Opera... including that it zooms everything, so I have to scroll horizontally...

Which is probably why it's faster. I guess it has something to do with the layout in relation to the font... like I said: the more complex the layout, the slower it is.

A bit OT, sorry, but do you mean that forcing the "Minimum Font Size" under "Advanced options" in FF font configuration doesn't work? (it does for me)

Oh, there is an "advanced" tab!
Thanks, that works...