Topbar Blocked by AdBlock Plus Using the Fanboy Annoyances List
I was having the same problem, and @Oded's comments helped me track it down. The problem is that https://meta.stackexchange.com/content/img/share-sprite-new.svg?v=2d10b452229b triggers on
/share-sprite- from the Fanboy Annoyances List in AdBlock Plus.
I've outlined two ways to fix this, but there are certainly others. Your mileage may vary.
To fix it, you can use Ctrl+Shift+V and click the red x to disable that filter altogether. This applies to all sites, not just StackExchange.
Create Filter Exception
Alternatively, you can open the Adblock Plus preferences with Ctrl+Shift+F and create a custom filter with finer-grained permissions that apply just to the StackExchange network and its CDN. For example:
There may be a more efficient way to specify the exception, as AdBlock Plus will mark this exception rule with a snail, but it will certainly get the job done. Your mileage with custom filters and regular expressions will certainly vary.