uBlock Origin
Wide-spectrum content blocker. Comes with some filter lists that block things such as adverts and tracking scripts.
Recommended setup
The default settings should be fine for most users. One filter list I would recommend adding is DandelionSprout's Legitimate URL Shortener Tool. It serves to remove tracking parameters from URLs, similarly to the browser extension ClearURLs. You can add it by clicking the "Import..." section of the "Filter lists" tab in uBlock Origin's settings and pasting in the link above.
Downloads
CanvasBlocker
Prevents websites from using certain JavaScript APIs (application programming interfaces) to track your browser by assigning it a unique ID or "fingerprint".
Recommended setup
Defaults should be fine. I've never needed to change anything from the defaults myself, and turning on additional protections risks breaking some website that use those APIs.
Downloads
Download for Firefox
Source code
Skip Redirect
Skips intermediary pages that some websites use when linking to other websites. These intermediary pages are often use to collect analytical data or display sketchy adverts.
Recommended setup
Default settings should be fine, but you may need to edit the parameters for certain websites you use. I haven't come across any issues myself, though.
Downloads
Download for Firefox
Source code
Indie Wiki Buddy
Fandom.com sucks ass. Indie Wiki Buddy helps you cut it out of your life by redirecting to independent wikis automatically and rendering Fandom wikis with BreezeWiki to cut out the laggy scripts and unnecessary content when an independent wiki isn't available.
Recommended setup
I would recommend setting it to notify you of independent wikis when you visit a Fandom wiki rather than redirecting automatically, just for flexibility. Other than that, the defaults are fine.
Downloads
Homepage with downloads
Source code
Augmented Steam
Shows you more price details and information about deals available for games, and gives you more tools to use while browsing to better seek out specific categories of product.
Recommended setup
Augmented Steam highlights various objects depending on things such as whether you already on them or whether they're on your wishlist. You may wish to adjust the colours it uses to fit your needs.
Downloads
Homepage with downloads
Source code
XKit Rewritten
XKit Rewritten provides various tweaks and quality of life improvements for Tumblr, such as checking the post limit and replacing tags on posts in bulk.
Recommended setup
Everything is disabled by default. I would recommend turning on "Anti-Capitalism", "Quick Reblog", "Vanilla Audio", "Vanilla Video", and "Limit Checker". Feel free to try all of them out and see what fits you best.
Downloads
Download for Firefox
Download for Chrome
Source code
As a bonus, check out enchanted-sword's dashboard-unfucker userscript, which reverts the dashboard from the Twitter clone design to the previous design.