Ubiquitous sites are those 3rd parties which resources are embedded in countless web pages. Your privacy exposure is sharply increased by such ubiquitous sites.
An obvious example is Facebook: the Facebook widgets to like something are embedded in countless web pages, and as such these widgets serve as excellent tracking devices for Facebook to build a profile of your browsing history.
This is also true for other entity such as Twitter, Google, Disqus, etc.
Recommended reading:
Internet Companies: Confusing Consumers for Profit (EFF)
uBlock Origin (uBO)'s dynamic filtering can help you foil the ability of ubiquitous servers from building a profile of your browsing habits.
Will use Facebook as an example. Facebook will still have the ability to track your browsing habits when using uBO with its default settings [see benchmark's raw data for Easy Mode: notice in the list of 3rd parties how facebook.net is ubiquitous].
First, we block Facebook-related hostnames globally, such that network requests to Facebook servers are blocked by default, everywhere (the first column is for global rules):
All suggested global block rules for Facebook:[1]
* facebook.net * block
* facebook.com * block
* fbcdn.net * block
These rules will cause Facebook to be blocked everywhere by default:
This will foil the ability of Facebook to gather data about your browsing habits through the embedding of Facebook's resources on countless websites.
Blocking Facebook when visiting Facebook is not ideal though, and there is no real benefit for doing so. Thus we will create an exception to the above global rules, but just for when we visit Facebook's own site (the second column is for local rules):
All suggested global noop rules for Facebook.[1]
facebook.com facebook.com * noop
facebook.com facebook.net * noop
facebook.com fbcdn.net * noop
The same sort of dynamic filtering rules can be used for whatever sites for which you still would want Facebook widgets to work:
example.com facebook.com * noop
example.com facebook.net * noop
example.com fbcdn.net * noop
This is just an example, the same can be applied to any of the ubiquitous servers out there. The dynamic filtering pane in uBO's popup UI will keep you informed about all the 3rd-party servers a web page connects (or tries to), and from there one can simply point-and-click to create global/local block/noop rules to foil the ability of 3rd parties to record your browsing history.
block rules to ubiquitous websites will easily reduce significantly your privacy exposure.
Using the above example of blocking Facebook everywhere with the benchmark result for Easy mode (uBO's default mode), the count of 3rd parties would have been decreased from 512 to 437, an easy way to significantly reduce your privacy exposure with just a few clicks.
[1] At time of writing. Ubiquitous servers may eventually change their hostnames or add new ones. As a good habit, regularly investigate which 3rd parties are embedded in the web pages you visit.