Network prediction features cause request leakage
First off, many thanks to @Bisaloo for testing beta1 of the WebExtension under uncommon conditions, and for finding and reporting this issue. It's great to see that the beta is being thoroughly tested!
Currently affected users
This issue affects early adopters of the beta for Firefox who have network prediction set to enabled, and are not using content blockers (e.g. uBlock Origin) that automatically disable this feature by default.
General problem description
Despite the fact that Decentraleyes properly redirects requests away from large CDNs, some settings cause browsers to attempt to predict your network traffic, and send requests out before noticing that the request is not supposed to occur. This feature can cause unnecessary request leakage.
Resolving the issue
You can fix the issue by rebuilding, and reinstalling Decentraleyes from the very latest commit inside of the master branch (7d21a1ed). The upcoming, packaged, release of beta1 will ship with the fix.