Almost perfect! Rated 5 out of 5 stars

***UPDATE*** - The below review was written without my realizing that the ability to right click individual toolbars and change icon size is **NOT** default Firefox behavior, but behavior that is added from an extension called "toolbarmode" by JSLover, which I installed quite some time ago and forgotten about. This extension has not been updated since 2011. So, the problem is due to that extension, not Classic Toolbar Buttons!

It would still be nice though to get the icon sizes per individual toolbar to retain when Firefox is restarted! :P

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This is **almost** perfect.

I'm currently on Firefox 26.0.For the longest time, I have struggled with the annoyance that I cannot have different toolbars, where some toolbars have large icons and some toolbars have small icons. I have to go to "View" -> "Toolbars" -> "Customize", then either select or deselect the "Use Small Icons" toggle checkbox. That means, ***usually***, that **all** (or **most**) toolbars will always end up reverting to small or large icons based on that checkbox, regardless if I right click a specific toolbar, select "Style/Icons" -> "Icons" -> "Small" or "Large".

For example, to reproduce this sort of thing, go to "View" -> "Toolbars" -> "Customize", then select the "Use Small Icons" toggle checkbox. Now right click any button on the navigation toolbar, select "Style/Icons" -> "Icons" -> "Large". You should now have large button icons on the navigation bar. Close Firefox, and restart it. You will see that the navigation toolbar has reverted back to small button icons.I was hoping that Classic Toolbar Buttons would solve this, but it hasn't!

This review is for a previous version of the add-on (1.3.5.1-signed). 

Mozilla uses a wrong description, there are no 'large' icons in Firefox since Firefox 4.0. 'Small icons' should be called 'small buttons' or 'small button shapes', because icons don't get changed anymore only paddings and margins around them. The back button is the only exception with a slightly larger icon.

CTB keeps compatibility to Firefox buttons and uses default icon sizes (16x16px-18x18px). If you are looking for large icons, you probably should check out 'full themes'.
https://addons.mozilla.org/en-us/firefox/complete-themes/