Firefox user here.

Bitwarden password manager
Bypass Paywalls Clean
Clear URLs remove URL trackers
Highlight or Hide Search Engine Results to hide some unwanted websites from search results
Open in VLC™ media player, useful for some weird streams
Push to Kindle sends any text article to PDF or to your ereader (not only Kindle)
Recipe Filter filters recipe pages on blogs and just gets the actual ingredients & instructions
Redirector for a few paywalls where I use a specific proxy
RSS Reader Extension (by Inoreader) - as I use Inoreader for following RSS feeds
Sci Hub Injector adds sci-hub links to many science publishing websites for easy access
Shinigami Eyes highlights trans-friendly and transphobic social media users or websites
uBlock Origin
ViolentMonkey for userscripts

Extensions to be helpful to other people:

Picket Line Notifier tells you if the website you are visiting has workers on strike - useful especially for ecommerce & news publishers
Snowflake is not noticeable for me, but allows other people to use my network as a Tor node or something idk
Wayback Machine archives every page I visit on the Internet Archive.

Fediverse extensions:

Youtube extensions:

Auto HD / 4k / 8k pour YouTube™ - I use it for the environment, so default quality is 480px (because usually I watch the videos on a small side window so it doesn't change the visible quality)
Clickbait Remover for YouTube - replaces thumbnails with a frame from the video and makes all titles normally named, no all caps
DF YouTube (Distraction Free) - removes the homepage & sidebar on videos to avoid rabbit holes
SponsorBlock auto-skips sponsored segments, intros, credit rolls, etc. on YouTube videos