There are many reports of people experiencing issues with some web sites,
or images not loading, etc. Turns out many of these are a result of using
some legacy extensions along uBO/webext. For instance, Reek's AAK in GreaseMonkey
has been causing issues with images not loading.

If you experience such issue, you will have to disable all your legacy extensions and
see if this fixes your issue. If so, then you will have to re-enable your legacy extension one
by one to find the one(s) causing the problem.

If you found that your issue is caused by one or more legacy extensions, there is nothing I can do.

Everything is moving to WebExtensions, so it might be just a good time to start
giving up on legacy extensions, they are not going to be supported at all
in a couple of weeks when Firefox 57 is released.

Another option is to install uBO 1.13.8 and disable auto-update for it.

There is also an issue specific to webext extensions, which can cause a web page
to load improperly: https://bugzilla.mozilla.org/show_bug.cgi?id=1396226.