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:

• FediAct allows me to boost, reply to, follow, etc. on any Mastodon instance without having to open the right link in my own instance. I wish there was something like this for Lemmy and Peertube.
• Fedishare allows for one-click sharing to several Fediverse platforms, including Lemmy and Mastodon
• PeerTubeify tries to check if a YouTube video you're watching is also on PeerTube

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