Firefox good or bad for ad click rates?

German online advertising company Adtech reported that Firefox users click on fewer ads than Internet Explorer users. In aggregate, 0.11% of Firefox users clicked on ads, versus 0.5% of IE users. (Info via this CNET story.) This is potentially worrying for Internet advertising (including search) companies and their investors, because Firefox is taking market share from IE. So what's happening?

Firefox has an integrated pop-up blocker, as does IE version 6 with
Windows XP Service Pack 2. But other versions of IE don't. As a result,
clicks on pop-up ads are much lower (like.. zero) with Firefox than
with IE. David Hallowell, a Mozilla contributor cited in the CNET
story, thinks that IE users inadvertantly click on pop-ups, whereas
Firefox users actually have higher click rates on contextual ads than
users of IE.

However, an article on Open Source points out that Firefox allows users to block images as well as pop-ups. Moreover, a downloadable extension, Adblock,
allows users to specify filters to remove unwanted content (ads) based
on the source-address. For example: all content from Doubleclick.
Adblock also allows users to block Google contextual ads, but Open
Source says "it is not recommended as it distorts the layout of the
webpage in most of the cases".

My gut feeling is that ad blocking technology will force advertisers
to provide ads that people actually want to see. Contextual
advertising, which is relevant to the content being viewed, will
probably gain share; branding advertising may be in for a rougher ride.

Initial thoughts on stock implications:
(1) The
elimination of pop-up ads may drive advertisers to contextual ads
provided by Google and Overture (Yahoo). If Firefox results in higher
click rates on contextual ads, Google and Yahoo could therefore
actually benefit.
(2) Pop-up ads are known to be highly cost
effective for advertisers. Eliminating pop-up ads will therefore raise
advertising costs for the less scrupulous advertisers who currently use
pop-ups. Incrementally negative for e-commerce companies that buy
pop-up ads.
(3) Firefox's superior ad blocking technology could hurt
the providers of banner ad networks, including Doubleclick and
Aquantive.