Make Firefox your default browser | Firefox Help - Mozilla Support Firefox will now be set as your default browser If Firefox was unable to make itself the default browser, it will open the Windows Settings Default apps panel (shown below), where you can click the entry under Web browser to choose Firefox as the default
Choose your preferred PDF viewer in Firefox | Firefox Help When Firefox is set as the default PDF viewer, it automatically opens PDF files in the built-in viewer However, you can choose to use another application to view your downloaded PD
Add or remove a search engine in Firefox | Firefox Help - Mozilla Support Mycroft Project search engine plugins The Mycroft Project website offers search engine plugins When you click an available search plugin, you can add it to Firefox from the Search bar or from the address bar context menu, on the Install plugin page
Mozilla Thunderbird marking my OUTGOING messages as spam (never . . . Not knowing all the details, I would try this: first, edit the DESCRIPTION field of BOTH of the RCN SMTP server settings pane to be UNIQUE from each other that can be your guarantee that you are not mismatching servers after doing that, click the account settings and highlight each account name and look at the bottom line on right side to see if the SMTP server link matches the unique
Change your default search settings in Firefox The Search panel in Firefox Settings lets you customize your search options You can add or remove search engines, change your default search engine, change address bar settings, assign or change keyword shortcuts, turn the search bar on or off and choose whether to display search suggestions first or not at all
Thunderbird and Gmail | Thunderbird Help - Mozilla Support Synchronizing folders (labels) If you want to see all your Gmail labels and messages in Thunderbird but prefer to avoid all the messages being downloaded to your system, you may want to tweak the synchronization settings