- In Firefox, go to Tools > Options > Content, and make sure "[x] Load Images" is checked. Click [Exceptions] to verify if images from a specific domain are filtered.
- In SeaMonkey, go to Edit > Preferences > Privacy & Security > Images and check your "Image Acceptance Policy" settings. Click [Manage Image Permissions] to look for per-domain settings.
If Adblock Plus blocks everything you probably have a faulty filter like "*.*" in your list. One reason this can happen is CyberSitter or a similar program corrupting download of the filter list. If you use CyberSitter: open the CyberSitter control panel, select "User Files" tab, then put the sites your filter subscriptions download from (e.g. "easylist.adblockplus.org" for EasyList/EasyElement) under "Always Allowable Sites". Open Adblock Plus preferences and choose Filters - Update all subscriptions from the menu to force an update of all subscriptions, the issues should be gone then.
If you cannot install Adblock Plus or any other extension because it doesn't get activated after restart or you keep getting "Unexpected installation error -203", the extension files in your Firefox profile are corrupted. Go to your Firefox profile and remove the files extensions.cache, extensions.ini, extensions.rdf. These files will be created again when you start Firefox, and you should be able to install extensions then.
If you think you have found a bug in an older version of Adblock Plus, please try installing the newest version from http://adblockplus.org/en/installation first, it may be fixed already.
If the problem doesn't go away (yikes!), don't hesitate to report it here, feedback is very much appreciated.
Please include both your browser's and Adblock Plus's exact version number, your operating system (exact too. e.g. what windows) the language your browser is set to and - if existing - your filter list subscription(s).
In case the problem occurs on a specific website, please don't let us guess and share a link
If possible, also give the steps needed to reproduce the problem (e.g. "Open Adblock Plus Preferences, click Add Filter..., enter *kermit*, browser turns green and makes strange croaking sounds").
The output in the error console may help speed up debugging a lot:
Clearing the console's content before provoking the error may make it easier for you to find the right error messages.